Highly filled high thermal conductive material, method for manufacturing same, composition, coating liquid and molded article

ABSTRACT

[Problem] Provided are a high filler-loaded high thermal conductive material which sufficiently utilizes features of an organic polymer while ameliorating drawbacks, enables integrated molding with ceramics, metals, semiconductor elements and the like, and has a low coefficient of thermal expansion and a high thermal conductivity; and a method for producing the high filler-loaded high thermal conductive material, a composition, coating liquid and a molded article. 
     [Solution] Disclosed is a high filler-loaded high thermal conductive material formed by subjecting a composition which includes organic polymer particles and a thermally conductive filler having a graphite-like structure, and includes 5 to 60% by weight of the organic polymer particles and 40 to 95% by weight of the thermally conductive filler having a graphite-like structure relative to 100% by weight of the total amount of these components, is obtained, so that the thermally conductive filler is dispersed by delamination while maintaining the average planar particle size of the thermally conductive filler, and is capable of forming a thermally conductive infinite cluster; to press molding at a temperature higher than equal to the deflection temperature under load, melting point or glass transition temperature of the organic polymer and a pressure of 1 to 1000 kgf/cm 2 ; and to cooling and solidification.

TECHNICAL FIELD

The present invention relates to a high filler-loaded high thermalconductive material, a method for producing the same, a composition, acoating liquid and a molded article.

BACKGROUND ART

Along with the performance enhancement, functional enhancement,miniaturization, and expansion of the range of applications ofelectronic equipment, the issue of heat associated with semiconductorelements such as CPU, driver elements, electronic transducers,thermoelectric conversion elements (Peltier cooling, Seebeck powergeneration) and light emitting elements (laser, LED, organic EL, and thelike) used therein, lithium ion batteries, fuel cells, and the like thatare used in the electronic equipment, has posed a significant problem.Thus, investigations have been conducted on the removal of this heat,from various aspects such as a material aspect and a structural aspect.

Furthermore, also for automobiles, which are used under severeconditions for environmental changes such as vibration and temperatureso that safety is emphasized, the heat dissipation problem that comeswith the progress of electronization and electrification has beenbrought into limelight. Thus, in addition to the demand for weightreduction, there is also a demand for the emergence of new materialswhich will replace metals, ceramics, and organic/inorganic compositematerials that have been conventionally used, and emergence anddiffusion of next-generation vehicles such as hybrid vehicles, electricvehicles and fuel cell vehicles are even accelerating this phenomenon.

In particular, organic polymers can be easily molded and processed andcan contribute to weight reduction, and various modifications thereofcan be easily made to meet the conditions of use associated withenvironmental changes. Therefore, there are high expectations on organicpolymers in the fields of automobiles and electronic equipment. However,since the thermal conductivities of organic polymers are as extremelylow as 0.1 to 0.5 W/mK, and the coefficients of thermal expansion arerelatively high such as 50×10⁻⁶ to 100×10⁻⁶° C.⁻¹, there is a problemwhen the organic polymers are used in combination with semiconductorelements, ceramics and the like having low coefficients of thermalexpansion (3×10⁻⁶ to 8×10⁻⁶° C.⁻¹). Thus, emergence of an innovativematerial having a high thermal conductivity and a low coefficient ofthermal expansion is earnestly desired.

Meanwhile, regarding heat conduction of materials, there are known threetypes of forms of conduction: (1) electronic conduction, (2) phononconduction (lattice vibration), and (3) photon conduction (radiation).For example, diamond, one of carbon materials, has a rigid, chemicallycombined structure without any heat loss, and has the highest thermalconductivity of 1000 to 2000 W/mK induced by phonon conduction. This isbecause there is no asymmetric chemical bond, or no loss of heat energycaused by molecular movement. Also, graphite (synonym for black lead)has a high thermal conductivity due to electron transfer in theorientation direction of benzene rings. More specifically, a PSGgraphite sheet has a thermal conductivity of 8 W/mK in the thicknessdirection, and a thermal conductivity of near 800 W/mK in the planedirection perpendicular to the thickness direction due to electrontransfer, and is therefore a conductive material. On the other hand,hexagonal boron nitride has a graphite-like structure, and exhibitsanisotropy by having a thermal conductivity of 200 W/mK in the planedirection and a thermal conductivity of some W/mK in the thicknessdirection; however, hexagonal boron nitride is an insulating material.Furthermore, regarding heat radiation which is photon conduction,organic polymer materials and carbon materials generally exhibit highervalues than metals. Furthermore, the coefficients of thermal expansionof carbon materials range from 1×10⁻⁶ to 5×10⁻⁶° C.⁻¹, which are lowerthan the coefficients of organic polymer materials (50×10⁻⁶ to 100×10⁻⁶°C.⁻¹) and closer to those of ceramics and semiconductor elements. Thus,carbon materials are low thermal expansion materials. In addition, metalmaterials have intermediate values such as 10×10⁻⁶ to 30×10⁻⁶° C.⁻¹.

Metals that have been traditionally used have excellent electricalconductivity and thermal conductivity; however, metals have highspecific gravity, have low heat radiation rates, and are inapt forprocessing into complicated shapes. Ceramics have excellent electricalinsulating properties; however, ceramics are brittle and unsuitable forprocessing into complicated shapes, and require high energy at the timeof production and at the time of processing.

Under such circumstances, in order to ameliorate these drawbacks,attention has been paid to the development of a composite materialformed from a thermally conductive material having a graphite-likestructure, and an organic polymer.

For example, Patent Literature 1 discloses a material obtained bybinding a mixture of a metal powder and carbon fiber using a fluorineresin in an amount of 0.5% to 20% by weight with respect to the mixture,and compression molding the mixture into a predetermined shape.According to Patent Literature 1, it is described that the materialobtained as described above has excellent thermal expansioncontrollability, thermal conductivity, and electrical conductivity.

Furthermore, Patent Literature 2 discloses a resin composition including10% to 60 by weight of a resin such as polyphenylene sulfide, and 40 to90% by weight of graphite having a particle size of 20 to 900 μm.According to Patent Literature 2, it is described that a molded articlehaving a thermal conductivity of 2 to 12 W/mK is obtained by injectionmolding or the like of the composition.

Furthermore, Patent Literature 3 discloses a high filler-loaded resincomposition including: (a) 5 to 50% by weight of a thermoplastic resin,and (b) 95 to 50% by weight of an inorganic filler, in which (c) any oneor more of a fatty acid metal salt, an ester-based compound, an amidegroup-containing compound, an epoxy-based compound, and a phosphoricacid ester is added in an amount of 0.5 to 10 parts by weight relativeto 100 parts by weight of the total amount of (a) and (b). According toPatent Literature 3, it is described that a molded article having athermal conductivity of 2 to 32 W/mK is obtained by injection molding ofthe composition.

Furthermore, Patent Literature 4 discloses, in order to suppress damageof carbon fiber in a kneading process, a method for producing a highthermal conductive resin composition obtainable by melt kneading shortcarbon fibers having an average fiber diameter of 5 to 20 μm and anaverage fiber length of 20 to 500 μm, and a matrix resin.

However, the material described in Patent Literature 1 contains a metalpowder as a main ingredient, and the characteristics of the carbon fiberand the resin are not sufficiently reflected.

Furthermore, the resin compositions and the like described in PatentLiteratures 2 to 4 basically involve melt kneading and molding athermally conductive filler and/or carbon fiber and an organic polymermaterial. Therefore, as a molten organic polymer material covers thesurface of the thermally conductive filler, formation of a thermallyconductive path is inhibited, and the characteristics such as thermalconductivity inherently possessed by the thermally conductive materialcannot be sufficiently exhibited.

On the contrary, Patent Literature 5 discloses a structure having athermal conductivity of 7 W/mK or more, in which polymer particles and acarbon filler containing carbon fiber as an essential component are drymixed so as to have a phase A formed from a polymer and a phase Bcontaining a carbon filler as a main component, and the phase B forms athree-dimensional network structure.

Furthermore, Patent Literature 6 discloses, in order to reduce damage ofhighly rigid carbon fiber, a powder molded article having excellentthermal conductivity, which includes 20 to 1000 parts by volume of apitch-based graphitized carbon fiber having an aspect ratio of 4 to 100and an average fiber length of 20 to 500 μm relative to 100 parts byvolume of a matrix component.

Patent Literatures 5 and 6 are both intended to obtain a structure or amolded article by dry blending (dry mixing)—compression molding (pressmolding). However, the carbon fiber used in the production of thestructure described in Patent Literature 5 is a special ultrafine carbonfiber (vapor grown carbon fiber) usually called carbon nanofiber, andrequires a special apparatus for the production, while the carbonnanofiber is highly expensive with limited uses. Furthermore, the powdermolded article described in Patent Literature 6 cannot sufficientlyexhibit the properties of the carbon fiber because, since theingredients are mixed so as to maintain the original fiber length,uniform mixing of the matrix resin and the carbon fiber is not achieved.

In addition, reports have been made on an attempt to acceleratecrystallization of a resin molded article by adding a crystallizationaccelerating agent, and to enhance the physical properties of a moldedbody.

For example, Patent Literature 7 discloses a high thermal conductivethermoplastic resin composition obtained by adding a thermallyconductive filler and a crystal nucleating agent to a thermoplasticresin having a mesogen group and a spacer.

Furthermore, Patent Literature 8 discloses that an ultrafine carbonfiber having a fiber diameter of 0.0001 to 5 μm and an aspect ratio of 5to 15,000 is used as a resin crystallization accelerating agent.

However, Patent Literatures 7 and 8 are intended to acceleratecrystallization of the resin by using a crystal nucleating agent such astalc, or a resin crystallization accelerating agent such as ultrafinecarbon fiber, and to enhance the physical properties of molded articles.Since a resin composition is melt blended, however, the features of thethermally conductive filler or carbon fiber cannot be sufficientlyutilized in an effective manner, and the Patent Literatures do notmention about crystallization of the resin and intensive formation ofthermal conduction paths.

On the other hand, in regard to an enhancement of thermal conduction byusing a crystalline aromatic thermosetting resin, Patent Literature 9discloses a resin composite composition including a benzoxazinederivative, a polycyclic aromatic type epoxy resin, and an inorganicfiller. However, there are no particular limitations on the moldingmethod except that template curing is carried out after melt blending,and there is no disclosure on a resin composite composition including athermoplastic resin.

CITATION LIST Patent Literatures

Patent Literature 1: JP-H09-153566 A

Patent Literature 2: JP-2004-339290 A

Patent Literature 3: JP-4631272 B

Patent Literature 4: JP-2012-82296 A

Patent Literature 5: JP-4963831 B

Patent Literature 6: JP-2010-24343 A

Patent Literature 7: JP-2011-231159 A

Patent Literature 8: JP-2004-339484 A

Patent Literature 9: JP-2011-231196 A

SUMMARY OF THE INVENTION

Organic polymers have excellent features that are not found in othermaterials; however, in composite materials thereof with thermallyconductive materials (thermally conductive fillers and short carbonfibers), the thermally conductive materials cannot sufficiently exhibitinherent properties intrinsically, such as high thermal conductivity.This is considered to be because the thermal conductivities of organicpolymers are extremely low, and since the organic polymers have highfluidity at the time of fusion, a thick thermal conduction inhibitingfilm is formed around the thermally conductive materials (a sea-islandstructure in which the polymer phase forms a sea, and the thermallyconductive material forms islands).

In this regard, when a polymer is fused and solidified in a state that athermally conductive material is not sufficiently uniformly dispersedand mixed, thermal conduction paths are formed. However, since thepolymer does not sufficiently penetrate into the thermally conductivematerial, a sea-island structure in which a portion of the polymer phaseforms islands is formed, and mechanical properties such as strength of amolded article are markedly deteriorated. Even in this case, theadvantages of organic polymers are not sufficiently manifested.

An object of the present invention is to solve this problem which is acontradictory trade-off, and to provide a high filler-loaded highthermal conductive material which exhibits features of an organicpolymer while ameliorating drawbacks thereof, enables integrated moldingwith ceramics, metals, semiconductor elements and the like, and has alow coefficient of thermal expansion and a high thermal conductivity; amethod for producing the material; and a composition and a moldedarticle thereof.

The inventors of the present invention repeated intensiveinvestigations, in order to solve the problems described above, on themethod for mixing and pulverization of a high thermal conductive fillerand organic polymer particles, and the relationship between thermalconductivity and the degree of crystallization (heat of fusion) of aresin. As a result, the inventors found that when a composition whichincludes a high thermal conductive filler having a graphite structureand organic polymer particles, is obtained by a particularmixing-pulverization method, and is capable of forming a thermallyconductive infinite cluster, is press molded under a predeterminedpressure at a temperature higher than or equal to the deflectiontemperature under load, melting point, or glass transition temperatureof the organic polymer, and the press-molded composition is cooled andsolidified in a state of having the morphology maintained,crystallization of the polymer occurs along the plane of the graphitestructure, and a high thermal conductive material having excellentproperties as a result of intensive formation of thermal conductionpaths is obtained. Thus, the inventors completed the present invention.

That is, the present invention solves the problem described above by thefollowing means.

(1) A high filler-loaded high thermal conductive material, formed bysubjecting a composition which includes organic polymer particles and athermally conductive filler having a graphite-like structure, andincludes 5 to 60% by weight of the organic polymer particles and 40 to95% by weight of the thermally conductive filler having a graphite-likestructure, relative to 100% by weight of the total amount of thosecomponents, is obtained, so that the thermally conductive filler isdispersed by delamination while maintaining the average planar particlesize of the thermally conductive filler, and is capable of forming athermally conductive infinite cluster; to press molding at a temperaturehigher than or equal to the deflection temperature under load, meltingpoint or glass transition temperature of the organic polymer and at apressure of 1 to 1000 kgf/cm²; and then to cooling and solidification;

(2) the high filler-loaded high thermal conductive material according to(1), wherein a ball mill is used as the means for dispersing thethermally conductive filler by delamination while maintaining theaverage planar particle size of the thermally conductive filler;

(3) the high filler-loaded high thermal conductive material according to(1) or (2), wherein the organic polymer particles contain at least oneselected from the group consisting of a thermoplastic resin, athermoplastic elastomer, and an uncrosslinked thermosetting resin, allof which have crystallinity and/or aromaticity, and the thermallyconductive filler having a graphite-like structure includes at least oneselected from the group consisting of natural graphite, artificialgraphite, and hexagonal boron nitride;

(4) the high filler-loaded high thermal conductive material according to(1) or (2), wherein the organic polymer particles are formed from atleast one selected from the group consisting of a thermoplastic resinand a thermoplastic elastomer, and an uncrosslinked thermosetting resinall of which have crystallinity and/or aromaticity;

(5) the high filler-loaded high thermal conductive material according to(1) or (2), wherein the organic polymer particles are formed from atleast one selected from the group consisting of a thermoplastic resinand a thermoplastic elastomer, both of which have crystallinity and/oraromaticity;

(6) the high filler-loaded high thermal conductive material according toany one of (1) to (5), wherein the average particle size of the organicpolymer particles is 1 to 5000 μm, the average particle size of thethermally conductive filler having a graphite-like structure is 0.5 to2000 μm, and the average particle size of the composition is 0.5 to 1000μm;

(7) the high filler-loaded high thermal conductive material according toany one of (1) to (5), wherein the average particle size of thethermally conductive filler having a graphite-like structure is 3 to 200μm, and the average particle size of the composition is 1 to 100 μm;

(8) the high filler-loaded high thermal conductive material according toany one of (1) to (7), wherein the thermally conductive filler having agraphite-like structure is natural graphite and/or artificial graphite,and has a thermal conductivity of 10 to 150 W/mK, a coefficient ofthermal expansion of 3×10⁻⁶ to 30×10⁻⁶° C.⁻¹, and a surface electricalconductivity of 5 to 250 (Ωcm)⁻¹;

(9) the high filler-loaded high thermal conductive material according toany one of (1) to (7), wherein the thermally conductive filler having agraphite-like structure is hexagonal boron nitride, and has a thermalconductivity of 5 to 50 W/mK, a coefficient of thermal expansion of3×10⁻⁶ to 30×10⁻⁶° C.⁻¹, and a surface electrical conductivity of 10⁻¹⁰(Ωcm)⁻¹ or less;

(10) the high filler-loaded high thermal conductive material accordingto any one of (1) to (9), wherein the organic polymer includes at leastone selected from the group consisting of polyphenylene sulfide,polyethylene terephthalate, polybutylene terephthalate, polycarbonateand benzoxazine, and the thermally conductive filler having agraphite-like structure includes scale-like graphite and/or hexagonalboron nitride;

(11) a method for producing a high filler-loaded high thermal conductivematerial, the method including:

-   -   (1) a step of preparing a composition which includes organic        polymer particles and a thermally conductive filler having a        graphite-like structure, includes 5 to 60% by weight of the        organic polymer particles and 40 to 95% by weight of the        thermally conductive filler having a graphite-like structure        relative to 100% by weight of the total amount of those        components, is obtained as the thermally conductive filler is        dispersed by delamination while maintaining the average planar        particle size of the thermally conductive filler, and is capable        of forming a thermally conductive infinite cluster;    -   (2) a step of press-molding the composition at a temperature        higher than or equal to the deflection temperature under load,        melting point or glass transition temperature of the organic        polymer and at a pressure of 1 to 1000 kgf/cm²; and    -   (3) a step of cooling and solidifying the material formed in the        step (2);

(12) the method for producing a high filler-loaded high thermalconductive material according to (11), wherein a ball mill is used asthe means for dispersing the thermally conductive filler by delaminationwhile maintaining the average planar particle size of the thermallyconductive filler;

(13) a high filler-loaded composition, capable of providing the highfiller-loaded thermal conductive material according to any one of claims1 to 10, or a high filler-loaded high thermal conductive materialproduced by the method according to (11) or (12);

(14) a coating liquid, including the high filler-loaded compositionaccording to (13) and a dispersing medium;

(15) the coating liquid according to (14), wherein the dispersing mediumincludes an oil-soluble organic medium and a water-soluble organicmedium.

(16) A molded article, containing the high filler-loaded high thermalconductive material according to any one of (1) to (10), a highfiller-loaded high thermal conductive material obtainable by theproduction method according to (11) or (12), or a high filler-loadedhigh thermal conductive material obtainable by applying and solid-dryingthe coating liquid according to (14) or (15), and being used as a highthermal conductive and heat dissipation component;

(17) the molded article according to (16), wherein the molded article isformed by laminating two layers of the high filler-loaded high thermalconductive material; one layer of the two layers has a thermalconductivity of 15 to 120 W/mK and a coefficient of thermal expansion of3×10⁻⁶ to 30×10⁻⁶° C.⁻¹, and exhibits electrical conductivity with asurface electrical conductivity of 10 to 200 (Ωcm)⁻¹; and the otherlayer of the two layers has a thermal conductivity of 5 to 50 W/mK ormore and a coefficient of thermal expansion of 3×10⁻⁶ to 10×10⁻⁶° C.⁻¹,and exhibits insulating properties with a surface electricalconductivity of 10⁻¹¹ (Ωcm)⁻¹ or less;

(18) the molded article according to (16) or (17), wherein the layers ofthe high filler-loaded high thermal conductive material are formed of agradient material.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph illustrating the relationship between the fillerconcentration and the thermal conductivity.

FIG. 2 is a graph illustrating the relationship between the fillerconcentration and the thermal conductivity.

FIG. 3 is a graph illustrating the relationship between the fillerconcentration and the thermal conductivity.

FIG. 4 is a graph illustrating the relationship between the fillerconcentration and the electrical conductivity.

FIG. 5 is a graph illustrating the relationship between the fillerconcentration and the heat of fusion.

FIG. 6 is a graph illustrating the relationship between the fillerconcentration and the heat of fusion.

FIG. 7 is a graph illustrating the relationship between the heat offusion per filler and the thermal conductivity.

FIG. 8 is a graph illustrating the relationship between the fillerconcentration and the coefficient of thermal expansion.

FIG. 9 is a SEM photograph of a graphite-PPS resin composition producedusing a ball mill.

FIG. 10 is a SEM photograph of a graphite raw material.

FIG. 11 is a SEM photograph of a short carbon fiber-PPS resincomposition produced using a ball mill.

FIG. 12 is a SEM photograph of a short carbon fiber raw material.

DESCRIPTION OF EMBODIMENTS

Embodiments for carrying out the present invention will be explained indetail hereinbelow.

According to an embodiment of the present invention, there is provided ahigh filler-loaded high thermal conductive material, formed bysubjecting a composition which includes organic polymer particles and athermally conductive filler having a graphite-like structure, includes 5to 60% by weight of the organic polymer particles and 40 to 95% byweight of the thermally conductive filler having a graphite-likestructure (hereinafter, also simply referred to as “thermally conductivefiller”), relative to 100% by weight of the total amount of thesecomponents, is obtained by a particular mixing/pulverization method, andis capable of forming a thermally conductive infinite cluster, to pressmolding at a temperature higher than or equal to the deflectiontemperature under load, melting point or glass transition temperature ofthe organic polymer and at a pressure of 1 to 1000 kgf/cm², and tocooling and solidification.

The high filler-loaded high thermal conductive material according to thepresent invention has a strongly entangled network of a high thermalconductive filler and an organic polymer established therein. Therefore,despite containing an organic polymer, the high filler-loaded highthermal conductive material is excellent not only in thermalconductivity, electrical characteristics, low thermal expandability, andmechanical properties, but is also excellent in lightweightness, easyprocessability, integrated moldability, durability against temperaturecycle, and the like. That is, a high filler-loaded high thermalconductive material which sufficiently utilizes features of an organicpolymer while ameliorating drawbacks, enables integrated molding withceramics, metals, semiconductor elements and the like, and has a lowcoefficient of thermal expansion and a high thermal conductivity; amethod for producing the same; a composition, a coating liquid, and amolded article can be provided.

<High Filler-Loaded High Thermal Conductive Material>

The high filler-loaded high thermal conductive material according to thepresent invention is a composite material containing an organic polymerand a thermally conductive filler having a graphite-like structure. Atthis time, the high filler-loaded high thermal conductive material issuch that its configuration is determined by the stages of formationthereof, and it is not appropriate to characterize the materialunambiguously by defining the organic polymer, the thermally conductivefiller, and the like. The reason for this is that, for example, the highfiller-loaded high thermal conductive material according to the presentembodiment has a nature in which it is difficult to define the degree ofpenetration of the organic polymer into the thermally conductive filler,uniformity of the thermally conductive filer, and the like, as will bedescribed below.

The thermal conductivity of the high filler-loaded high thermalconductive material according to the present embodiment is preferably 10to 150 W/mK, more preferably 15 to 100 W/mK, and even more preferably 15to 80 W/mK.

Furthermore, the coefficient of thermal expansion of the highfiller-loaded high thermal conductive material according to the presentembodiment is preferably 3×10⁻⁶ to 30×10⁻⁶° C.⁻¹. According to anembodiment of the present invention, in the case of using the highfiller-loaded high thermal conductive material in an application inwhich the material is brought into contact with a material having asmaller coefficient of thermal expansion, such as a semiconductorelement or a ceramic substrate, the coefficient of thermal expansion ismore preferably 3×10⁻⁶ to 20×10⁻⁶° C.⁻¹. According to another embodimentof the present invention, in the case of using the high filler-loadedhigh thermal conductive material in an application in which the materialis brought into contact with a heat dissipation component formed from ametal such as aluminum or copper, the coefficient of thermal expansionis more preferably 10×10⁻⁶ to 30×10⁻⁶° C.⁻¹.

Furthermore, according to an embodiment of the present invention, thesurface electrical conductivity of the high filler-loaded high thermalconductive electroconductive material (when the thermally conductivefiller is graphite) according to the present embodiment is preferably 5to 250 (Ωcm)⁻¹, more preferably 10 to 150 (Ωcm)⁻¹, and even morepreferably 20 to 150 (Ωcm)⁻¹.

Moreover, according to another embodiment of the present invention, thethermal conductivity of the high filler-loaded high thermal conductiveinsulating material (when the thermally conductive filler is hexagonalboron nitride) is preferably 5 to 50 W/mK. Also, the surface electricalconductivity is preferably 10⁻¹⁰ (Ωcm)⁻¹ or less, and more preferably10⁻¹⁵ to 10⁻¹¹ (Ωcm)⁻¹.

[Composition]

(Contents of Components and Figures)

The composition used for the formation of the high filler-loaded highthermal conductive material includes organic polymer particles and athermally conductive filler having a graphite-like structure, andincludes 5 to 60% by weight of the organic polymer particles and 40 to95% by weight of the thermally conductive filler having a graphite-likestructure (thermally conductive filler) relative to 100% by weight ofthe total amount of these components. At this time, the composition isobtained so that the thermally conductive filler is dispersed bydelamination while maintaining the average planar particle size of thethermally conductive filler. Also, the composition meets the conditionsfor forming a thermally conductive infinite cluster. Furthermore, knownadditives may also be added to the composition as necessary.

The thermally conductive filler having a graphite-like structure is inthe form of particles having a layered structure, and is an anisotropicmaterial in which the materials in the layers are connected by strongbonding in the plane direction of the layers, and are connected by weakbonding between the layers. Since the thermally conductive filler havinga graphite-like structure is likely to be shifted in the planardirection, the filler can be used as a lubricating/mold releasingmaterial. Here, the term “delamination” means that detachment occursbetween layers that are connected by weak bonding, while the state ofconnection in the planar direction of the thermally conductive filler ismaintained unchanged. Thereby, the average planar particle size of thethermally conductive filler can be maintained, and the thermallyconductive filler can be dispersed in the composition. Meanwhile, in thepresent specification, the “planar particle size” means the particlesize in the planar direction of a particle having a layered structure,and the “average planar particle size” means the average value of theplanar particle sizes in the planar direction. For the average planarparticle size, values measured by an image analysis with opticalmicroscopy, electron microscopy and the like will be employed. Also,according to the present specification, the phrase “the average planarparticle size is maintained” means that the degree of reduction of theaverage planar particle size is ½ or less.

Furthermore, the term “infinite cluster” is based on the percolationtheory, and in general, the “percolation theory” is a theory on how anobject substance is connected in a system, and how the features of theconnection are reflected in the nature of the system. Specifically, whenthe filler particles are sufficiently brought into contact with oneanother to reach the percolation (penetration) threshold, the fillerparticles are aggregated to a concentration higher than or equal to aparticular concentration (threshold) of the electrically conductivefiller to form a cluster in which the entire system stretches out(infinite cluster). Then, electrical conductivity is exhibited over theentire system.

In the present invention, it was found that the figure such ascrystallinity and compatibility of the organic polymer that exists inthe vicinity of the thermally conductive filler particularly largelyaffects not only electrical conductivity, but also thermal conductivityand thermal expandability. Meanwhile, it is contemplated that thepercolation threshold depends on the concentration and shape of thethermally conductive filler, the state of mixing with the organicpolymer particles, and the state of bonding between the thermallyconductive filler particles. However, electrical conductivity isstrongly affected by the shape of the filler or polarity of the resin ascompared with thermal conductivity, and thereby, electrical conductivityis more sensitive.

According to the present embodiment, the composition meets theconditions for forming a thermally conductive infinite cluster, andthese conditions can be realized by controlling the contents of theorganic polymer particles and the thermally conductive filler in thecomposition, and uniform dispersibility, shape, morphology and the likeof the respective components.

Whether the composition according to the present embodiment meets theconditions for forming an infinite cluster is determined as follows.That is, in regard to the composition described above, the issue can bedirectly determined by forming a high filler-loaded high thermalconductive material by a method described below, and observing themicrostructure of the high filler-loaded high thermal conductivematerial using a scanning electron microscope (SEM) or a transmissionelectron microscope (TEM). Furthermore, the issue can be indirectlydetermined from a exponential increase in the physical properties whenthe thermal conductivity and/or electrical conductivity of the materialis/are plotted, or from the controllability of the coefficient ofthermal expansion of the material when the coefficient of thermalexpansion is plotted.

(Organic Polymer Particles)

The average particle size of the organic polymer particles used in thepresent invention is usually 1 to 5000 μm, and preferably 5 to 500 μm.When the average particle size of the organic polymer particles is 1 μmor more, no special apparatus for micronization is needed. On the otherhand, when the average particle size of the organic polymer particles is5000 μm or less, defective dispersion is not likely to occur. Organicpolymer particles including lumpy objects having a large particle sizecan be used after being pretreated in advance by pulverization and/orcrushing, classification and the like to obtain a desired averageparticle size.

The organic polymer particles preferably have an aromatic hydrocarbonstructure similar to the thermally conductive filler having agraphite-like structure, and it is particularly preferable tocrystallize the organic polymer around the filler particles in thepresence of the filler, along the planar direction of the filler.

Examples of the organic polymer particles that can be used includethermoplastic resins having crystallinity and/or aromaticitythermoplastic polymers, uncrosslinked elastomers, and thermosettingpolymers being uncured thermosetting resins, all of which are used inthe field of molding.

Examples of crystalline aromatic thermoplastic resins include knownthermoplastic polymers having crystallinity and aromaticity, such asaromatic polyesters such as polyethylene terephthalate (PET),polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT),polyethylene naphthalate (PEN), and liquid crystal polyester (LCP);polyphenylene sulfide (PPS), aromatic polyimide (PI) precursors, phenol(novolac type and the like) phenoxy resins, polyether ketone (PEK),polyether ether ketone (PEEK), polystyrene, polybenzimidazole, andpolyphenylene oxide. These resins are particularly preferable becausethe resins can strongly fix the filler particle between filler particlesdue to the crystalline of the polymer grown onto the filler surface,and/or compatibility with the filler; electrical conductivity orinsulating properties, and thermal conductivity can be markedlyincreased without significantly impairing mechanical properties; and thecoefficient of thermal expansion can be appropriately controlled.

Examples of crystalline thermoplastic resins include known thermoplasticpolymers having crystallinity, such as polyolefins such as polyethylene(PE) and polypropylene (PP); polyoxymethylene (POM), polyamide (PA),polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidenechloride, polyketone (PK); fluororesins such as polytetrafluoroethylene(PTFE); cycyloolefin polymers, polyacetal, and ultrahigh molecularweight polyethylene. These resins are preferable because the resins canfix the filler particle between filler particles through crystallizationof the polymers grown onto the filler surfaces, electrical conductivityor insulating properties, and thermal conductivity can be increasedwithout impairing mechanical properties, and the coefficient of thermalexpansion can be controlled.

Examples of non-crystalline aromatic thermoplastic resins include knownthermoplastic polymers having aromatic substituents, such aspolycarbonate (PC), polyphenylene ether (PPE), polyallylate (PA),polysulfone (PSU), polyether sulfone (PES), polyether imide (PEI),polyamideimide (PAI), and liquid crystal polymers. Since these resinshave a structure similar to that of thermally conductive fillers, theresins are crystallized, in the presence of a thermally conductivefiller, on the surface and/or in the vicinity of the thermallyconductive filler, or even if crystallization is not attained as a wholesystem, the resins have high compatibility with the thermally conductivefiller having a similar structure. Therefore, the resins are preferablebecause they can increase the electrical conductivity or insulatingproperties and thermal conductivity and can control the coefficient ofthermal expansion without significantly impairing mechanical properties,by fixing the filler particle between filler particles on the surfaceand/or in the vicinity of the filler. It is preferable to use uncuredthermosetting resins in combination with the thermoplastic resinsdescribed above, rather than to use alone, from the viewpoints ofadjusting the viscosity upon melting, or increasing theadhesiveness/compatibility between filler particles or between differentkinds of materials.

Examples of uncrosslinked elastomers include known elastomers, such asthermoplastic elastomers having aromatic substituents and/or crystallineolefin moieties, such as polystyrene-based, polyolefin-based,polyurethane-based, polyester-based, polyamide-based,polybutadiene-based, polyisoprene-based, silicone-based, andfluorine-based elastomers; and thermoplastic elastomers having aromaticsubstituents and/or crystalline olefin moieties, including graftcopolymers containing olefin-based polymer segments formed from α-olefinmonomers and vinyl-based polymer segments formed from vinyl-basedmonomers.

Examples of uncured thermosetting resins include known thermosettingresin precursors, such as unsaturated polyesters, vinyl esters, epoxies,phenols (resol type), urea/melamine, polyimide, benzoxazine, all ofwhich have aromatic substituents. Since the thermosetting resinprecursors are usually oligomers having small molecular weights, whenthe precursors are used in combination with thermoplastic polymersand/or thermoplastic elastomers having large molecular weights, fluidityin the system is increased before curing, thereby increasingpenetrability of the polymer in between the filler layers. Furthermore,adhesiveness between filler particles or between different kinds ofmaterials is enhanced by the functional groups formed along with thecuring reaction. In addition, when the precursors are used incombination with engineering plastics having high melting points, themolding temperature can be decreased significantly. At this time, it ismore effective to use a product obtained by uniformly dispersing athermosetting resin precursor in a solvent in which an engineeringplastic is dissolved once.

Whether the composition meets the conditions for forming an infinitecluster, that is, whether the organic polymer establishes, in thepresence of a thermally conductive filler, a partially crystallinestructure around the filler particles, and the composition forms athermally conductive infinite cluster based on the thermally conductivefiller, can be directly observed using electron microscopy such asscanning electron microscopy (SEM) or transmission electron microscopy(TEM) as described above. Furthermore, the issue can be indirectlydetermined by measuring the heat of fusion of a molded specimen. Forexample, FIG. 7 illustrates the relationship between the thermalconductivities of aromatic crystalline resins excluding polycarbonateand polyethylene, and the heat of fusion per filler. According to FIG.7, it is understood that the thermal conductivity increases along withan increase in the heat of fusion per filler. Regarding a polycarbonate,which is an aromatic non-crystalline resin, a molded specimen does notexhibit any melting point if not aged, and has a small heat of fusion;however, a polycarbonate obtained immediately after a condensationreaction exhibits a heat of fusion of the same level as that of anaromatic crystalline resin. That is, it is speculated that in the fillersurface having a graphite-like structure, which induces crystallizationof a resin, crystallization occurs at a high level, and a high thermalconductivity will be exhibited. It can be said that the same applies tothermosetting resin precursors such as benzoxazine. Polyethylene is notan aromatic resin; however, since polyethylene exhibits high heat offusion, it is speculated that polyethylene may provide a thermalconductivity close to that of an aromatic resin. As such,crystallization of a resin around filler significantly affects thethermal conductivity of the material. It is essential for the organicpolymer particles used in the present invention to be crystallized inthe raw material and/or a molded article, and it is necessary for theorganic polymer particles to present the heat of fusion in any form.

The thermoplastic resin, uncrosslinked elastomer and uncuredthermosetting resin, described above, all of which have crystallinityand/or aromaticity as described above, may be copolymers or modificationproducts, and may also be a resin obtained by blending two or more kindsthereof. Furthermore, for an enhancement of impact resistance, a resinobtained by adding an elastomer or a rubber component to thethermosetting resin may also be used.

Among these thermosetting resins, particularly benzoxazine has excellentthermal resistance, and since curing proceeds as a result of an additionreaction, volatile side products are not generated. Further, thereaction also proceeds in the absence of catalyst, and a uniform andcompact resin phase can be formed, which is preferable.

The benzoxazine described above is a compound having adihydro-1,3-benzoxazine ring (hereinafter, also simply referred to as“oxazine ring”), and is a condensate of amines, phenols, andformaldehydes. Usually, the chemical structure of benzoxazine producedis determined by the substituents, kinds and the like of phenols, aminesand the like, which are reaction raw materials thereof. The benzoxazineused in the present invention may be any derivative of an “oxazinering”, and is not particularly limited; however, a compound having atleast two oxazine rings in one molecule is preferred. This is becausethe crosslinking density is increased, and superior results such as anenhancement of thermal resistance are obtained. Specific examples ofbenzoxazine include Pd type benzoxazine and Fa type benzoxazine,manufactured by Shikoku Chemicals Corp.

Regarding the amines for deriving benzoxazine having at least twooxazine rings, diamines can be used. Examples of the diamines include4,4′-oxydianiline, 4,4′-diaminodiphenylmethane, para-diaminobenzene, andcompounds obtained by substituting the foregoing compounds with an alkylgroup, an alkoxy group, a halogen, an aromatic hydrocarbon group and thelike. Among these, it is preferable to use 4,4′-diaminodiphenylmethane.

Examples of phenols include, as monovalent phenols, phenol, cresol,xylenol, and naphthol; and as polyvalent phenols, bisphenol; andcompounds obtained by substituting the foregoing compounds with an alkylgroup, an alkoxy group, a halogen, an aromatic hydrocarbon group, andthe like. Specific examples of bisphenol include bisphenol A, bisphenolF, and bisphenol S. Among these, it is preferable to use phenol andbisphenol.

Regarding formaldehydes, formaldehyde (aqueous solution),para-formaldehyde and the like are used. Among these, it is preferableto use formaldehyde.

In order to obtain benzoxazine from the amines, phenols, andformaldehydes described above, a wide variety of known methods can beemployed.

A benzoxazine having at least two oxazine rings can be produced by amethod of allowing a diamine, a phenol, and a formaldehyde to react; amethod of allowing a bisphenol, a primary amine, and a formaldehyde toreact; or the like.

The organic polymer particles formed from a thermoplastic resin, athermoplastic elastomer or a thermosetting resin areuncrosslinked/uncured particles in the mixture. As will be described,when the mixture is heated and molded under pressure, the thermoplasticresin may be crosslinked, and the thermoplastic elastomer orthermosetting resin before being crosslinked/cured is usually used.

Examples of the elastomer used for the purpose of modification includenatural rubber, isoprene rubber, styrene-butadiene rubber, butadienerubber, chloroprene rubber, nitrile rubber, butyl rubber,ethylene-propylene rubber, urethane rubber, silicone rubber, acrylicrubber, chlorosulfonated polyethylene rubber, fluorine rubber,hydrogenated nitrile rubber, epichlorohydrin rubber, and polysulfiderubber.

Among these organic polymer particles, for organic polymer particlesthat have high thermal resistance, strongly fix the filler particlebetween filler particles, and enhance various physical properties suchas heat conductivity and electrical characteristics, polyethyleneterephthalate, polybutylene terephthalate, polyphenylene sulfide,polycarbonate, and benzoxazine are suitable. When the various polymerparticles described above are used in combination in accordance with thepurpose of use, the features of organic polymers can be manifested atthe maximum.

(Thermally Conductive Filler Having Graphite-Like Structure)

The thermally conductive filler used in the present invention has agraphite-like structure. Regarding the thermally conductive filler,known thermally conductive fillers which are used in the field ofmolding and are formed from black leads (synonym for graphite) thatusually have electrical conductivity, such as natural graphite such asscale-like graphite, bulk graphite and soil graphite, artificialgraphite, and expanded graphite; thermally conductive ceramics thatusually have insulating properties, such as hexagonal boron nitride,hexagonal silicon carbide, and hexagonal silicon nitride; and mixturesthereof, can be used without any particular limitations. Among these,scale-like graphite and hexagonal boron nitride are particularlypreferred because they produce high thermal conductive materials havinghigh electrical conductivity or high insulating properties,respectively.

Regarding the black leads, furthermore, a product obtainable bypulverizing an artificial graphite electrode, a product obtainable bygraphitizing powdered cokes by a heat treatment at 3000° C., a productobtainable by cutting and pulverizing a graphite sheet, a graphitepowder obtainable by making scale-like graphite into a spherical form,and a recycled product obtainable by heat treating carbon fibers thathave been used or has become a waste material, can also be used.

Natural graphite is originally a mineral produced as ancient creaturesand plants are buried in the earth and denatured under the effect ofground heat or ground pressure for a long time before being putrefiedand decomposed, as in the cases of petroleum and coal. The element thatconstitutes the majority of natural graphite is carbon, but silicondioxide, aluminum oxide and the like are included therein in traceamounts as other impurities. Examples of the natural graphite includescale-like graphite, bulk graphite, and soil graphite.

The scale-like graphite is scale-shaped graphite produced mainly frommines in China, the United States, India, Brazil and the like and havinga large aspect ratio, and in general, larger scales are associated withhigher thermal resistance. Graphite having an average particle size ofabout 8 to 200 μm and a carbon content of 85 to 99% is frequently soldin the market, and this graphite is anisotropic but has a high thermalconductivity of 200 W/mK or more.

Bulk graphite is a natural graphite in a bulk state produced in SriLanka, and bulk graphite is produced from a mineral vein having acontent of about 95%, compared with scale-like graphite whose content inrocks is ten-several %. Since the particles are bulky, the aspect ratiois small.

Soil graphite is clod-like graphite produced mainly in China, SouthKorea and North Korea, and is used in many fields because soil graphitehas high affinity with moisture compared with scale-like graphite. Agraphite having an average particle size of about 5 to 20 μm and acarbon content of 80 to 90% is commercially available.

Artificial graphite is a graphite obtained by molding a mixture ofpowdered cokes and pitch, and artificially developing crystals through ahigh temperature calcination process at about 3000° C., and thisgraphite has fewer impurities and high hardness.

Expanded graphite is a graphite obtained by applying heat toacid-treated scale-like graphite to expand graphite crystals betweenlayers to several hundred times. Since expanded graphite has a very lowspecific gravity while having the characteristics of scale-likegraphite, and has fewer impurities, expanded graphite is used as fillerin various fields.

Hexagonal boron nitride is a white powder having a scale-like crystalstructure resembling graphite, and is a chemically stable materialcalled “white graphite”. Hexagonal boron nitride is a material havingexcellent thermal conductivity, thermal resistance, corrosionresistance, electrical insulating properties and lubricating/moldreleasing properties, and is widely used as an additive material invarious matrices. Thus, known materials can be used as received. Ascale-like form or a polygonal plate form is generally used, and thereare also available aggregate powders in which primary particles arecompositely aggregated; however, hexagonal boron nitride of scale-likeform is preferred. Although the substance is anisotropic, a molded bodythereof has a high thermal conductivity of about 60 W/mK.

Silicon carbide can be roughly divided into two kinds such as hexagonalα-type silicon carbide and cubic β-type silicon carbide. Silicon carbideis electrically insulating and has high hardness and a high thermalconductivity, and thus, application thereof as a structural materialutilizing high hardness is underway, in addition to application as aheat generator or a varistor utilizing semiconductivity. These basiclayer structures adopt a closest packed structure and are distinguishedby the difference in the period of stacking of layers. Among these, theβ-type silicon carbide is limited to one kind of sphalerite (zincblende) structure in which a half of carbon (C) in the diamond structureis substituted by silicon (Si). On the other hand, the α-type siliconcarbide is based on a wurtzite (wurtzite) type crystal structure. Theα-type crystal structure of silicon carbide can be described as stackingof a basic layer structure spread along the bottom surface, and ispreferable as the thermally conductive filler used in the presentinvention.

Silicon nitride is a colorless compound, and only silicon nitride havinga composition of Si₃N₄ is considered as a stable phase. There are threekinds of forms such as α-type of hexagonal crystal, β-type of trigonalcrystal, and amorphous form. Amorphous silicon nitride is produced at arelatively low temperature, and the composition is not always constant.The amorphous type is converted to the α-type when heated. The α-type isa low temperature phase and is irreversibly transferred to the β-type at1400° C. to 1600° C. The β-type is stable up to high temperatures, butis thermally decomposed at 1800° C. to 1900° C. Silicon nitride is avery hard material having excellent sliding properties and also havingexcellent thermal resistance and corrosion resistance, and exhibitssuperior performance in various abrasion resistance members, slidingmembers, high temperature structural members, and corrosion resistancemembers. Furthermore, silicon nitride has high thermal conductivity thatis greater than or equal to that of iron, and can also be imparted withelectrical conductivity depending on the composition. Therefore, siliconnitride is a very unique high-tech ceramic which can be applied tovarious functional members. For the thermally conductive filler used inthe present invention, the α-type of hexagonal crystal is preferred.

The average particle size of the high thermally conductive filler havinga graphite-like structure of the present invention is 1 to 2000 μm, andpreferably 3 to 200 μm. When the average particle size of the thermallyconductive filler is 1 μm or more, the surface area is decreased, andthe loss of heat and electrical conduction at the filler interface canbe reduced. On the other hand, when the average particle size of thethermally conductive filler is 2000 μm or less, it is preferable becausedefective dispersion is not likely to occur.

For a filler including lumpy objects having large particle sizes, it ispreferable to use the filler after pretreating the filler in advance bypulverization and/or crushing, classification and the like, andadjusting the particles to a desired average particle size. Combined useof thermally conductive fillers having different particle sizes, andknown methods for promoting an increase in thermal conductivity bycontrolling the filler shape can also be used.

(Method for Preparing Composition)

The composition according to the present embodiment can be prepared bymixing, after crushing if needed, 5 to 60% by weight of organic polymerparticles and 40 to 95% by weight of a thermally conductive fillerhaving a graphite-like structure. However, when the materials are mixedusing an excessively large force, particle size reduction occurs; forthis reason, the surface area of the thermally conductive fillerincreases significantly, and inhibition of thermal conduction occurs atthe particle interfaces, which is not preferable. Thus, in the presentembodiment, it is preferable to mix the materials by a method ofuniformly dispersing the thermally conductive filler in the compositionwhile maintaining the average planar particle size of the thermallyconductive filler. An example of the mixing method may be a method ofusing delamination. Meanwhile, the composition may include knownadditives in addition to the organic polymer particles and the thermallyconductive filler.

Examples of the method of mixing the organic polymer particles, thethermally conductive filler and the like include a method of introducingthe materials into a bag or a can and manually mixing the materials; amethod of using a tumbler or the like; a method of using a powder mixingmachine such as a Henschel mixer, a Super mixer, or a high-speed mixer;a method of using a pulverizing machine such as a jet mill, an impactmill, an attrition mill, an air classification (ACM) mill, a ball mill,a roller mill, a bead mill, a medium mill, a centrifuge mill, a conemill, a disc mill, a hammer mill, or a pin mill; and methods combiningthese.

The method of manually mixing or the method of using a tumbler does notinvolve large force such as shear force between the powder particles,and therefore can prevent damage or deformation of powder. However, fromthe viewpoint of eliminating vacant spaces (voids) between the fillerparticles (therefore, the density is increased) by sufficientlyuniformly mixing the respective fine particles of the organic polymerparticles and the thermally conductive filler, and allowing the organicpolymer to sufficiently penetrate between the filler particles, andthereby forming a thermally conductive infinite cluster sufficiently, itis preferable to carry out the mixing by methods other than the methodof manual mixing and a method of using a tumbler.

The method of using a mixing machine and/or a pulverizing machine iscapable of uniform mixing because large forces such as compressiveforce, shear force, impact force and frictional force are applied topowder particles, and is preferable for the present invention. Amongthese mixing machines and/or pulverizing machines, it is preferable touse a ball mill. A ball mill is an apparatus for producing a powderdispersed by grinding down a material adhering to ball surfaces usingfrictional force or impact force, by introducing hard balls made of aceramic or the like and powders of materials into a cylindrical vessel,and rotating the vessel. Therefore, dispersion can be achieved bydelamination while maintaining the planar particle size of the fillerlayers as far as possible. As a result, the ball mill is particularlypreferable for mixing and/or pulverization of the thermally conductivefiller of the present invention having a layered structure. For example,FIGS. 9 to 12 show scale-like graphite and short carbon fibers used asraw materials, and SEM photographs of compositions obtained by mixingthese fillers with PPS by a ball mill. Scale-like graphite having alayered structure almost maintains the particle size of the rawmaterials even after being pulverized and mixed with a ball mill, andexhibits a high thermal conductivity. However, in the case of shortcarbon fiber having a rod shape, particle size reduction occurs tomarkedly decrease the thermal conductivity.

It is not particularly necessary to strictly control the size or shapeof the raw materials used at the time of mixing and pulverization;however, it is preferable to use a size or shape in a preliminarilydetermined range in order to maintain the product quality.

The mixing time is not particularly limited, but the mixing time ispreferably 0.2 to 15 hours, and more preferably 0.5 to 5 hours.

Furthermore, the average particle size of a uniform composition (organicpolymer particles and a thermally conductive filler) obtained by mixingand/or pulverization is preferably 0.5 to 1000 μm, and more preferably 1to 500 μm. When the average particle size of the composition is 0.5 μmor more, the contact area between filler particles is decreased as aresult of a decrease in the surface area to prevent deterioration ofthermal conductivity and electrical characteristics caused by the lossinduced by contact. On the other hand, when the average particle size ofthe composition is 1000 μm or less, the resin is uniformly dispersed toprevent a decrease in strength caused by defective contact between theresin and the filler.

For the measurement of the average particle sizes of the organic polymerparticles and the thermally conductive filler used as raw materials, andof the organic polymer particles and the thermally conductive filler inthe composition, known methods such as a dynamic light scatteringmethod, a laser diffraction method, an imaging method using opticalmicroscopy/electron microscopy, and a gravity sedimentation method canbe used. Furthermore, the level of delamination can be directlydetermined by optical microscopy or electron microscopy, or can beindirectly determined by measuring the thermal conductivity, electricalconductivity, coefficient of thermal expansion, mechanical propertiesand the like of the material.

The proportion of the organic polymer particles in the composition ofthe present invention is 5 to 60% by weight, and preferably 10 to 50% byweight. If the proportion of the organic polymer particles is less than5% by weight, a decrease in strength caused by defective dispersion ofthe thermally conductive filler, or the like occurs. On the other hand,the proportion of the organic polymer particles is more than 60% byweight, thermal conduction paths are not easily formed (the percolationthreshold is not reached), and this leads to a rapid decrease in thermalconductivity (however, even in a case in which the proportion of theorganic polymer particles is 60% by weight or less, an infinite clustermay not be formed depending on the state of mixing or the like).

On the other hand, the proportion of the thermally conductive filler inthe composition is 40 to 95% by weight, and preferably 50 to 90% byweight. If the proportion of the thermally conductive filler is lessthan 40% by weight, a thermally conductive infinite cluster is noteasily produced, and significant deterioration of physical propertiessuch as thermal conductivity, electrical characteristics and low thermalexpandability occur, which is not preferable. On the other hand, if theproportion of the thermally conductive filler is more than 95% byweight, defective dispersion of the thermally conductive filler occursto markedly deteriorate mechanical properties such as strength, which isnot preferable.

In the composition of the present invention, known additives,reinforcing agents, and/or fillers can be appropriately used asnecessary, to the extent that the addition does not cause contradictionto the purpose of the present invention. Examples of the additivesinclude a mold releasing agent, a flame retardant, an oxidationinhibitor, an emulsifier, a softening agent, a plasticizing agent, asurfactant, a coupling agent, and a compatibilizer. Examples of thereinforcing materials include short fibers formed from glass fiber,carbon fiber, metal fibers, and inorganic fibers. Examples of otherfillers include calcium carbonate (limestone), glass, talc, silica,mica, metal powders, metal oxides, aluminum nitride, boron nitride,silicon nitride, diamond, and recycled products obtainable by heattreating carbon fiber that has been used or has become a waste material.

[Press Molding of Composition, Cooling and Solidification]

The high filler-loaded high thermal conductive material of the presentinvention can be obtained by press molding the composition describedabove at a temperature higher than or equal to the deflectiontemperature under load, melting point or glass transition temperature ofthe organic polymer and at a pressure of 1 to 1000 kgf/cm², and coolingand solidifying the material thus obtained. Meanwhile, when a vacuum isapplied or pressure is reduced inside the mold at the time of hot pressmolding, air or gas bubbles included in the raw material compositioninside the mold, or the gas bubbles generated at the time of pressmolding can be eliminated, and various physical properties such asthermal conductivity of the molded article can be enhanced, which ispreferable.

The press molding can be carried out using known hot pressing methodssuch as compression molding using a mold, and sheet molding using hotrolls. At this time, it is necessary to use a raw material compositionthat is not melt mixed, and to melt the raw material composition insidea mold or by roll heating, whereby the thermally conductive filler canbe impregnated by molten polymer. Also, the organic polymer can becrystallized by cooling and solidification to form thermal conductionpaths at a high level between the thermally conductive fillers.

The pressure of the press molding is 1 to 1000 kgf/cm², and preferably10 to 500 kgf/cm². When the pressure of the press molding is 1 kgf/cm²or less, voids are not eliminated, and a compact molded article cannotbe obtained. On the other hand, when the pressure of the press moldingis 1000 kgf/cm² or more, the liquefied or softened polymer leaks throughgaps of the mold, and mold release is not easily achieved.

Here, the differences between a raw material, a composition, a materialand a molded article are such that the raw material is a crude material;the composition is an indeterminately shaped raw material mixture(powder) in which various raw materials are uniformly dispersed andmixed; a material is an indeterminately shaped solid obtainable from thecomposition and is not limited in shape; and the molded article refersto a solid having a certain shape.

When the composition is heated at a temperature higher than or equal tothe deflection temperature under load, melting point or glass transitiontemperature of the organic polymer, the organic polymer particles can beliquefied or softened. Thereby, the liquefied or softened polymer can becaused to infiltrate itself into the gaps between one filler particleand another filler particle, and a phase A formed from only the organicpolymer and a phase B containing the filler as a main component areentangled, so that the phase B forms a three-dimensional networkstructure. Since the thermally conductive filler concentration is higherthan or equal to the percolation threshold, the thermally conductivefillers are in sufficient contact with each other on the layer end facesof the thermally conductive filler, and the thermally conductive fillerexists as a cluster spreading over the entire system. In a coolingstage, cold from the outside starts to cool the phase B containing thefiller that has significantly high thermal conductivity, and then causessolidification and/or crystallization of the polymer in thesurroundings. Thus, efficient solidification/immobilization around thefillers occurs.

In particular, since the filler having a graphite structure and anaromatic crystalline resin as a preferred organic polymer have similarstructures, crystallization proceeds along the layer surface. Then, bycovering the surroundings of the filler layers by the crystal structureof the polymer, the gaps between the filler layer end faces that areconsidered to be filled with non-crystalline polymer are immobilized ina sufficiently compactly contacting manner, and thus thermal conductionpaths can be formed at a high level.

Regarding the temperature at the time of press molding, the meltingpoint is used for a crystalline polymer, the glass transitiontemperature is used for a non-crystalline polymer, and when the meltingpoint or glass transition temperature is not defined or absent, thedeflection temperature under load is used as the measure, while atemperature higher than or equal to those is used. Meanwhile, thedeflection temperature under load, melting temperature and glasstransition temperature differ depending on the kind of the organicpolymer used.

Next, the material obtained by press molding is cooled and solidified.

The cooling temperature is not particularly limited, but it is atemperature at which the organic polymer is solidified, where themelting point, glass transition temperature and deflection temperatureunder load of the organic polymer are taken as a reference. The coolingtemperature is preferably 0 to 100° C., and more preferably 10 to 50° C.

Furthermore, the cooling time is not particularly limited, but ispreferably 0.05 to 3 hours, and more preferably 0.5 to 1.5 hours.

The degree of crystallization of the organic polymer can be determinedby taking the heat of fusion obtainable using a differential scanningcalorimeter (DSC), as an indicator. The degree of crystallization of athermally conductive filler-containing organic polymer can berepresented as the heat of fusion per resin and the heat of fusion perfiller; however, the former usually decreases as the thermallyconductive filler concentration increases. This is because it ispredicted that along with an increase in the thermally conductive fillerconcentration, an amorphous polymer exists in a large amount between thethermally conductive filler layer end faces where crystallization is notlikely to occur. The heat of fusion per filler is the heat of fusion perresin corresponding to the parts by weight of the filler, and is theeffective amount of the heat of fusion (crystal) that contributes to thethermal conductivity. Even for an organic polymer which is classified asan amorphous organic polymer, if the raw material powder before moldinghas the heat of fusion (when polymerization from a monomer to a polymerproceeds, an optimal structure that is likely to be crystallized can bereasonably adopted), rearrangement of molecules occurs as a result ofannealing, and the organic polymer manifests the heat of fusion. Thatis, this implies that even for a polymer which is classified as anamorphous organic polymer, if the polymer has aromatic groups,crystallization occurs on the thermally conductive filler surface havinga graphite-like structure, and the gaps between the thermally conductivefiller layer end faces can be immobilized.

<Method for Producing High Filler-Loaded High Thermal ConductiveMaterial>

According to an embodiment of the present invention, a method forproducing a high filler-loaded high thermal conductive material isprovided. This production method includes: (1) a step of preparing acomposition which includes organic polymer particles and a thermallyconductive filler having a graphite-like structure, includes 5 to 60% byweight of the organic polymer particles and 40 to 95% by weight of thethermally conductive filler having a graphite-like structure, relativeto 100% by weight of the total amount of these components, is obtainedso that the thermally conductive filler is dispersed by delaminationwhile maintaining the average planar particle size of the thermallyconductive filler, and is capable of forming a thermally conductiveinfinite cluster; (2) a step of press molding the composition at atemperature higher than or equal to the deflection temperature underload, melting point or glass transition temperature of the organicpolymer and at a pressure of 1 to 1000 kgf/cm²; and (3) a step ofcooling and solidifying the material formed in the step (2).

For the above described steps (1) to (3), the above-described method canbe appropriately employed.

<High Filler-Loaded Composition>

According to an embodiment of the present invention, a highfiller-loaded composition as a powder mixture is provided. This highfiller-loaded composition provides the high filler-loaded high thermalconductive material mentioned above. In addition to that, thecomposition may also include the above-mentioned known additives,reinforcing agents and/or fillers, for example, a mold releasing agent,a flame retardant, an oxidation inhibitor, an emulsifier, a softeningagent, a plasticizing agent, a surfactant, a coupling agent, acompatibilizer; short fibers formed from glass fiber, carbon fiber,metal fibers inorganic fibers; calcium carbonate (limestone), glass,talc, silica, mica, metal powders, metal oxides, aluminum nitride, boronnitride, silicon nitride, diamond, and recycled products obtainable byheat treating carbon fiber that has been used or has become a wastematerial. In regard to the high filler-loaded composition, thedescriptions related to the composition described above areappropriately applied.

<Coating Liquid>

According to another embodiment of the present invention, a coatingliquid is provided. This coating liquid also provides the highfiller-loaded high thermal conductive material described above. Thecoating liquid includes a high filler-loaded composition and adispersing medium. This coating liquid can produce a uniform film orcoating layer of a high thermal conductive material having a filmthickness of 10 mm or less by applying the coating liquid on asubstrate, and then removing the dispersing medium using a means such asheating or pressure reduction. The coating liquid can also be utilizedas an adhesive.

Examples of the dispersing medium include water (boiling point: 100° C.)media; oil-soluble organic media such as methyl ethyl ketone (boilingpoint: 80° C.), toluene (boiling point: 111° C.), phenol (boiling point:182° C.), and tetralin (boiling point: 207° C.); water-soluble organicmedia such as t-butanol (boiling point: 82° C.) and ethylene glycol(boiling point: 196° C.); and medium mixtures thereof.

The boiling point of the dispersing solvent used is preferably 70° C. to200° C. When the boiling point is 70° C. or higher, there is no risk offire caused by evaporation of the dispersing solvent, or aggravation ofthe work environment. When the boiling point is 200° C. or lower, asignificant decrease in the thermal conductivity caused by residualdispersing medium can be prevented.

In the case of using a water medium, since aggregation or separation ofthe high filler-loaded composition can easily occur, dispersionstabilizers such as an emulsifier and a dispersant are usually used.Since many of these dispersion stabilizers adversely affect the physicalproperties such as electrical characteristics and thermal conductivity,it is preferable to use an organic medium having satisfactory dispersionstability. Regarding the cautions to be taken in the case of using anorganic medium, when a dispersing medium and/or dispersion conditions inwhich the organic polymer dissolves are used, the organic polymer coatsthe peripheries of the thermally conductive filler particles or forms asingle film of the organic polymer to inhibit the formation of athermally conductive cluster. For this reason, it is necessary toappropriately select an appropriate organic medium and a combinationthereof, or the dispersion conditions such as the dispersion temperatureand the dispersing method. In particular, a combination of anoil-soluble medium and a water-soluble medium is preferred becausedissolution of the organic polymer can be prevented while uniformdispersion of the composition is maintained. It is particularlypreferable to use a mixed medium dispersion liquid in which an organicpolymer has been precipitated by adding dropwise a solution of organicpolymer particles in an oil-soluble medium, into a water-soluble mediumin which a thermally conductive filler is dispersed.

In regard to the method for dispersing a high filler-loaded compositionand a dispersing medium, known methods capable of uniform mixing/uniformdispersing, such as dispersing methods of using mechanical dispersionsuch as a homomixer or a homogenizer, or ultrasonication, can be used.The concentration of the high filler-loaded composition in the coatingliquid is preferably 10 to 50% by weight. When the concentration of thehigh filler-loaded composition in the coating liquid is 10% by weight ormore, separation between the organic polymer and the thermallyconductive filler does not easily occur, and when the concentration is50% by weight or less, it is easier to produce a uniform thin film bydilution. Even in the case of using an organic medium, known dispersionstabilizers can be used to the extent that the properties of the highthermal conductive material are not adversely affected.

Furthermore, the high filler-loaded composition can be used in theproduction of molded articles including sheets, films and the like thatwill be described below.

<Molded Article>

Molded articles according to the present invention include sheets, filmsand the like, and a known powder molding method of shaping a material ina powdered state and heating and molding the material, for example, ahot press molding method can be used. A molded article having a shapeaccording to the application can be easily obtained by using a moldwhich gives a desired shape. In particular, when a sheet or a film isproduced, it is preferable to use the material impregnated with acoating liquid or a dispersing medium. Also, a molded article having amultiphase structure or a gradient structure, for example, an integratedmolded article having a biphasic structure composed of an insulatingphase and an electroconductive phase, or a gradient structure includingan insulating phase and electroconductive phases having different fillerconcentrations, can be obtained by using different materials as moldingraw materials. At this time, use can be made of known methods such as amethod of separately shaping compositions formed from various materialsin a powdered state, and molding the resultants at the end to obtain anintegrated molded article; and a method of molding compositions formedfrom various materials in different stages, and obtaining an integratedmolded article at the end. In this manner, the difference in thecoefficient of thermal expansion between a semiconductor element and aceramic substrate or a metal heat dissipation component can be madesmall.

Furthermore, a molded article can also be formed using a highfiller-loaded high thermal conductive material obtained by a method ofapplying and solid-drying the above-described coating liquid on a basematerial.

The proportions of the organic polymer and the thermally conductivefiller in the molded article are basically the same as those in thecomposition, except for the non-woven fabric used as a reinforcingmaterial at the time of molding, and also similarly to the case of thecomposition, the molded article can contain known additives, reinforcingpreparations and/or other fillers as necessary, to the extent that theinclusion does not cause contradiction to the purpose of the presentinvention. Examples of the additives include a mold releasing agent, aflame retardant, an oxidation inhibitor, an emulsifier, a softeningagent, a plasticizer, a surfactant, a coupling agent, and acompatibilizer. Examples of the reinforcing materials include shortfibers formed from glass fiber, carbon fiber, metal fibers and inorganicfibers, and non-woven fabrics formed from these fibers, and recycledproducts obtainable by heat treating carbon fiber that has been used orhas become a waste material. Examples of the other fillers includecalcium carbonate (limestone), glass, talc, silica, mica, metal powders,metal oxides, aluminum nitride, boron nitride, silicon nitride, anddiamond. These additives, reinforcing agents and/or other fillers aregenerally used by being added to a raw material mixture; however, whenused as a reinforcing material, in the case of fiber, a non-woven fabricor the like, it is preferable to use the reinforcing material in thestage of molding.

Since the high thermal conductive material and molded article of thepresent invention are configured as above, despite being a highfiller-loaded thermally conductive material, a high thermal conductivematerial or a molded article having, for example, in the case of usinggraphite, a thermal conductivity of 10 to 150 W/mK, a coefficient ofthermal expansion of 3×10⁻⁶ to 30×10⁻⁶° C.⁻¹, and a surface electricalconductivity of 5 to 200 (Ωcm)⁻¹ while maintaining the mechanicalstrength, is preferred. On the other hand, in the case of usinghexagonal boron nitride, a material having a thermal conductivity of 5to 50 W/mK, a coefficient of thermal expansion of 3×10⁻⁶ to 30×10⁻⁶°C.⁻¹, and an electrical conductivity of 10⁻¹⁰ (Ωcm)⁻¹ or less ispreferred. Therefore, it is also possible to impart other functions suchas electrical conductivity, insulating properties, and electromagneticwave shielding properties in accordance with the intended use.Furthermore, since the polymer phase has a three-dimensionally entangledstructure, in the case of using a thermoplastic resin and athermoplastic elastomer as the organic polymer, a molded article of thepresent invention and another molded article formed from apolymer-containing material can be easily joined by ultrasonic weldingor spin welding. Furthermore, since the difference in the coefficient ofthermal expansion between materials can be made as small as possible,production of various products having satisfactory stability againstthermal cycles reaching from a low temperature to a high temperature andreaching from a high temperature to a low temperature, and havingvarious shapes and performances suitable for the intended use, isenabled. In particular, by using a gradient material, that is, amaterial in which plural materials having different compositions andstructures are continuously changed and integrally combined, a moldedarticle having small strain between materials can be provided byintegral molding of a material having a small coefficient of thermalexpansion such as a semiconductor element or a ceramic substrate, and amaterial having a large coefficient of thermal expansion such asaluminum or copper.

According to a preferred embodiment, the molded article is preferablyformed such that the high filler-loaded high thermal conductive materialis composed of two layers such as a layer having insulating propertiesand a layer having electrical conductivity being laminated. At thistime, it is preferable that one layer of the two layers has a thermalconductivity of 15 to 120 W/mK and a coefficient of thermal expansion of3×10⁻⁶ to 30×10⁻⁶° C.⁻¹, and exhibits electrical conductivity with asurface electrical conductivity of 10 to 200 (Ωm)⁻¹. Furthermore, it ispreferable that the other layer of the two layers has a thermalconductivity of 5 to 50 W/mK or more and a coefficient of thermalexpansion of 3×10⁻⁶ to 10×10⁻⁶° C.⁻¹, and exhibits insulating propertieswith an electrical conductivity of 10⁻¹¹ (Ωcm)⁻¹ or less. At this time,the various layers of the high filler-loaded high thermal conductivematerial exhibiting electrical conductivity or insulating properties canbe made of a gradient material, whereby the difference in thecoefficient of thermal expansion at the interface of materials ofdifferent kinds can be made as small as possible. Since the moldedarticle of the present invention exists in a state in which the organicpolymer is uniformly mixed therein, perforation or cutting into variousshapes can be easily achieved, and microprocessing with high accuracycan be carried out.

As such, by using the high thermal conductive material and moldedarticle of the present invention enable strong joining without any lossin thermal conductivity, and enable packaging of components withoutusing grease, an adhesive, a phase changing material, bolted joint orthe like, whereby, the numbers of components and operation processes canbe reduced to a large extent in the joining between different materialsand between molded articles. Furthermore, since the high thermalconductive material has a high thermal emittance that is close to thatof a blackbody as compared with ceramics and metals, heat dissipationcharacteristics that fairly exceed the thermal conductivity inherentlypossessed by the material itself can be manifested.

A molded article obtainable in this manner can exhibit features such asthe lightweightness, molding processability, cutting processability,integrated moldability, dimensional stability possessed by the organicpolymer, and improvements of physical properties in accordance with theapplication, while making the best of the features of the thermallyconductive filler having a graphite-like structure used therein. Forexample, the molded article is useful in high heat dissipationapplications, metal replacement applications, ceramic replacementapplications, electromagnetic wave shielding applications, highprecision components (low dimensional change), high electricalconduction applications, insulating applications, various gaskets, andthe like. Specifically, the molded article is useful forelectric/electronic components represented by various cases, gear casesLED lamp-related components, lithium ion battery-related components,fuel cell-related components, connectors, relay cases, switches,variable condenser cases, optical pickup lens holders, optical pickupslide bases, various terminal boards, transformers, printed wiringboards, liquid crystal panel frames, power modules and housings thereof,plastic magnets, semiconductor element substrates and related heatdissipation components, liquid crystal display components, lamp coversfor projectors and the like, FDD carriages, FDD chassis, actuators, HDDcomponents such as chassis, computer-related components, and the like;domestic and office electric appliance components represented by VTRcomponents, television components, irons, hair dryers, rice cookercomponents, microwave oven components, audio components, sound equipmentcomponents such as Audio Laserdisc (registered trademark) and compactdisc/digital videodiscs, lighting components, refrigerator components,and air conditioner components; optical equipment/precisionmachine-related components represented by office computer-relatedcomponents, telephone-related components, mobile telephone-relatedcomponents, facsimile-related components, printer/copyingmachine-related components such as print head peripheries and transferrolls, cleaning tools, motor components, microscopes, binoculars,cameras, timepieces and the like; automobile/vehicle-related componentssuch as alternator terminals, alternator connectors, IC regulators,potentiometer bases for light dimmer, motor core sealing materials,insulator members, power seat gear housings, thermostat bases for airconditioning, air conditioner panel switchboards, horn terminals,electrical component insulating boards, lamp housings, LED lamp heatdissipation components, lithium ion battery heat dissipation components,fuel cell separators, and ignition device cases; a wide variety ofhousing fields represented by personal computer housings, mobiletelephone housings, and housing applications for components such as tipantennas, installation antennas requiring shielding properties forelectromagnetic waves in information and communication field, and thelike; moreover, bulkhead plating requiring high dimensional accuracy,electromagnetic wave shielding properties, and barrier properties forgas, liquid and the like, applications requiring thermal and electricalconductivity or insulating properties, and automobile part applications,airplane part applications, electric/electronic component applications,thermal equipment component applications and the like, which areusefully used in equipment for outdoor installation or constructionmembers, and in which weight reduction and the degree of freedom inshape are required, and metal replacement is eagerly desired.

EXAMPLES

Hereinafter, the present invention will be specifically explained by wayof Examples, Comparative Examples and Reference Examples, but the scopeof the present invention is not intended to be limited to these.Meanwhile, production and evaluation of raw materials and specimens werecarried out as follows.

(1) Raw Materials:

[Organic Polymer Particles]

Polyphenylene sulfide (PPS) powder: W203A NATURAL manufactured by KurehaCorp., white powder, linear form, particle size 100 to 500 μm, meltingpoint 296° C., heat of fusion 33 J/g, coefficient of thermal expansion50×10⁻⁶° C.⁻¹

Polyphenylene sulfide (PPS) pellet: FZ-2100BK manufactured by DIC Corp.,black pellet, crosslinked type, shape: about 1.5 mm in innerdiameter×about 2 mm in length, melting point 280° C., heat of fusion 28J/g, coefficient of thermal expansion 40×10⁻⁶° C.⁻¹

Polyethylene terephthalate (PET): waste PET bottle recycled product,white flakes, particle size 1 to 2 mm, melting point 254° C., heat offusion 31 J/g, coefficient of thermal expansion 60×10⁻⁶° C.⁻¹

Polycarbonate (PC): NATURAL manufactured by Kasima Polymers Corp., whiteflakes, particle size 0.1 to 0.5 mm, melting point 236° C., heat offusion 26 J/g, coefficient of thermal expansion 70×10⁻⁶° C.⁻¹

Polyethylene (PE): low melting point PE, SANWAX 161-P, manufactured bySanyo Chemical Industries, Ltd., white powder, particle size 0.01 to 0.1mm, melting point 110° C., heat of fusion 25 J/g, coefficient of thermalexpansion 110×10⁻⁶° C.⁻¹

Benzoxazine: P-d type benzoxazine manufactured by Shikoku ChemicalsCorp., powder, particle size 0.01 to 0.1 mm, melting point 242° C., heatof fusion 25 J/g

[Thermally Conductive Filler Having Graphite-Like Structure]

Scale-like graphite (GF): BF-40K manufactured by Chuetsu Graphite WorksCo., Ltd., scale-like black powder, average particle size 40 μm, thermalconductivity 150 to 200 W/mK

Boron nitride (BN): hexagonal boron nitride simple grain type UHP-2manufactured by Showa Denko K.K., average particle size 9 to 12 μm,molded article thermal conductivity 60 W/mK

[Other Thermal Conductive Material]

Short carbon fiber: DIALEAD K223HE manufactured by Mitsubishi Plastics,Inc., pitch-based carbon fiber, cylinder-shaped, average fiber length 6mm, fiber diameter 11 μm, thermal conductivity 550 W/mK

[Other Filler]

Aluminum nitride: high purity H grade manufactured by Tokuyama Corp.,white powder, average particle size about 3 μm, thermal conductivity 180to 200 W/mK, coefficient of thermal expansion 4.2×10⁻¹° C.⁻⁶

(2) Measurement of Melting Point and Heat of Fusion of Polymer:

Portions of raw materials and molded article specimens produced with amold were collected, and the heat generation behavior was analyzed usinga differential scanning calorimeter DSC8230 manufactured by Rigaku Corp.The endotherm peak temperature (° C.) and the heat of fusion per resin(J/g resin) were determined, and these were taken as the bases for themelting point (° C.) and the degree of crystallization, respectively.Furthermore, the heat of fusion per resin corresponding to parts byweight of the filler was determined to multiply the heat of fusion perresin (J/g resin) with the weight proportion (wt %÷100) of the thermallyconductive filler. This was taken as the heat of fusion per filler (J/gresin), and was employed as a measure for the crystalline portion of theresin existing around filler particles.

(3) Measurement of Average Particle Sizes of Raw Materials andComposition:

The average particle sizes were measured based on measurement of theaverage particle size from the particle size at the degree of cumulationof 50% using a laser diffraction type particle size distributionanalyzer LA-500.

Alternatively, the average particle sizes were expressed as approximatevalues in a range of the particle size based on SEM or a magnifierobservations.

(4) Observation by Scanning Electron Microscopy (SEM):

The particle sizes and shapes of raw materials and compositions wereobserved using a scanning electron microscope (SEM) S-4800 (resolution:1.0 nm, accelerating voltage: 0.5 to 30 kV, magnification: ×20 to800,000) manufactured by Hitachi, Ltd.

(5) Measurement of Density:

A composition powder was introduced into a mold for specimen productionto a predetermined thickness, and was heated under pressure at apredetermined temperature for a predetermined time using a disk typehydraulic heat press machine. Thus, a molded article specimen wasproduced. The density was determined from the weight and volume of thespecimen. On the other hand, the density of the molded article specimenobtained using a twin-screw extruder was measured by a water immersionmethod.

(6) Measurement of Thermal Conductivity and Electrical Conductivity:

The thermal conductivity of a molded article specimen was measured usinga thermal property analyzer by a hot disc method (TPS2500S) manufacturedby Kyoto Electronics Manufacturing Co., Ltd. A hot disc method takesconsideration of making measurement to the extent that heat generatedfrom a hot disc sensor is transferred to the interior of a specimen, andthe heat does not reach to the end of the specimen. Thus, the hot discmethod is to measure thermal conductivity in the range from the surfaceof a specimen to a certain depth. Furthermore, the electricalconductivity at the surface and a cross-section of the same specimen wasmeasured according to JIS K7194 using a low resistivity meter, LorestaGP (four-point probe method) manufactured by Mitsubishi ChemicalAnalytech Co., Ltd. When the electrical conductivity was 10⁻⁷ (Ωcm)⁻¹ orless (measurement limit), the volume resistivity was measured accordingto JIS K6271 using a high resistivity meter manufactured by MitsubishiChemical Analytech Co., Ltd., HIRESTA UX type MCP-T800 (double ringelectrode method), and the volume resistivity was used after beingconverted to electrical conductivity (Ωcm)⁻¹ (corresponding tocross-sectional electrical conductivity) (measurement limit 10⁻¹⁵(Ωcm)⁻¹).

(7) Measurement of Coefficient of Thermal Expansion:

A molded article specimen obtained by hot press molding was cut toproduce a measurement sample having a size of about 3.6 mm inheight×about 3.6 mm in width×13 mm or less in length. The specimen washeated using a thermal expansion analyzer (TMA60) manufactured byShimadzu Corp. at a rate of 5° C./min, and the coefficient of thermalexpansion was measured in a temperature range of 27 to 180° C. at every10 minutes. For Examples and Comparative Examples, the values of thecoefficient of thermal expansion at 160° C. were described.

(8) Bending Test

A molded article specimen obtained by hot press molding was cut toproduce a measurement sample having a size of about 10 mm in width×about10 mm in thickness×about 40 mm in length. Bending strength and flexuralmodulus of elasticity were measured according to JIS K7171 using auniversal testing machine (AG-100kNE type) manufactured by ShimadzuCorp. Meanwhile, the dimension of the measurement samples (ComparativeExamples 3 to 8) for the molding test obtained using a twin-screwextruder was 10 mm in width×4 mm in thickness×80 mm in length.

(9) Heat Dissipation Test

In a thermostatic chamber set at an ambient temperature of 30° C., aheat dissipation component having a comb-type fin structure wasinstalled with the fin parts facing upward. A heater of 7.68 W, in whichthe heater part was sealed with polyimide, was fixed using acommercially available thermally conductive silicone grease or highthermal conductive insulating material between the heater and the heatdissipation component. Inside the thermostatic chamber, the heater wasinstalled so as to have the heater part in the lower side, andtemperatures were measured by fixing thermocouples, with the samepolyimide tape, at three sites including the interface between theheater part and the atmosphere, the interface between the heatdissipation component base immediately above and right next to theheater and the atmosphere, and the interface between the tips of theheat dissipation component fins and the atmosphere. The temperaturemeasurement values were input to a data logger, temperature changes weremeasured, and the time taken to reach an equilibrium state, thetemperature (T₁) of the heater part, the temperature (T₂) at a siteimmediately above and right next to the heater, the temperature (T₃) ofthe tips of the fins, and the ambient temperature (T₄) of thethermostatic chamber at that time were measured to obtain the thermalresistance (R=ΔT/W) between various temperatures. The obtained thermalresistance is taken as the reference for heat dissipationcharacteristics.

Examples 1 to 4 and Comparative Examples 1 and 2

A high filler-loaded composition was produced and cast in a powderedstate using a mold and a hot pressing machine, and press molding wascarried out under pressure and under heating to produce a specimen(molded article). Specifically, scale-like graphite and polyphenylenesulfide (PPS) powders at the contents expressed in wt % in Table 1 wereintroduced into a magnetic pot of a disk type ball mill BM-10manufactured by Seiwa Giken Co., Ltd., and the contents were pulverizedand mixed for 5 hours using magnetic balls to obtain a uniformcomposition. At this time, the particle size of the composition thusobtained was determined by microscopic observation by SEM.

Next, about 20 to 30 g of the composition was weighed and introducedinto a mold having a size of 40 mm in length×40 mm in width to obtain amolded article thickness of about 10 mm, and press molding was carriedout using a hot pressing machine by heating to a mold settingtemperature of 340° C. at a rate of 5° C./min under pressure at 5 to 10MPa (51 to 102 kgf/cm²), while adjusting the pressure so as to preventliquid leakage, and then maintaining the state for 30 minutes.Thereafter, the molded article was cooled to 20° C. for 0.5 hours andsolidified, and thus a high filler-loaded high thermal conductivematerial specimen was obtained.

The density, thermal conductivity, and electrical conductivity of thespecimen (molded article) thus obtained were measured by the methodsdescribed above. Also, a specimen was cut from the molded product, andanalyses of the coefficient of linear expansion, bending strength,flexural modulus of elasticity, heat of fusion per resin, and heat offusion per filler were carried out by the methods described above. Theresults thus obtained are presented in the following Table 1.

TABLE 1 Comparative Example Example 1 2 3 4 1 2 Com- PPS powder 60 50 305 70 2 position (wt %) Scale-like 40 50 70 95 30 98 graphite (wt %)Mixing Ball mill/powder mixing method Average 20 to 20 to 20 to 20 to 20to 20 to particle size 60 60 60 60 60 60 (μm) Molded Density 1.55 1.651.78 1.92 1.50 Impos- article (g/cm²) sible Thermal 15.5 25.2 38.2 62.23.70 to be conductivity molded (W/mK) Surface 0.85 1.39 25.8 120 0.29electrical conductivity ((Ωcm)⁻¹) Cross- 0.25 0.61 2.40 17.5 0.10section electrical conductivity ((Ωcm)⁻¹) Coefficient 40.5 29.8 12.31.95 43.7 of thermal expansion (×10⁻⁶° C.⁻¹) Bending 43 43 41 45 45strength (MPa) Flexural 3.2 3.0 3.0 3.4 3.4 modulus of elasticity (GPa)Heat of 35 38 31 18 33 fusion per resin (J/g resin) Heat of 14.0 19.021.7 17.1 9.9 fusion per filler (J/g resin)

As is obvious from the results of the above Table 1, it was found thatthe high filler-loaded high thermal conductive materials (moldedarticles) of Examples 1 to 4 had excellent heat conductivities,electrical conductivities and coefficients of linear thermal expansion,even in the case where the materials contained organic polymers, ascompared with the molded article of Comparative Example 1. Furthermore,regarding the bending strength and flexural modulus of elasticity,results similar to Comparative Example 1 that contained a large amountof the organic polymer were obtained. In Comparative Example 2 having avery low content of the organic polymer, shaping was achieved, butdisintegration occurred even under slight force, and a molded articlewas not obtained (bending strength and flexural modulus of elasticitycould not be measured). As such, it was found that the Examples weresuperior to the Comparative Examples. Furthermore, it was found that thecoefficient of thermal expansion decreased when the concentration of thethermally conductive filler (scale-like graphite) increased, and thusthe coefficient of thermal expansion can be controlled by theconcentration of the thermally conductive filler. In addition, a SEMphotograph of the scale-like graphite-PPS resin mixture of Example 4obtained by performing powder mixing with a ball mill, and a SEMphotograph of scale-like graphite used as a raw material are presentedin FIG. 9 and FIG. 10. It was found that even if pulverized and mixedwith a ball mill, the flat scale-like shape of graphite was maintained,and one half or more of the average planar particle size was maintained.From a comparison between the results described above and the thermalconductivity, electrical conductivity, coefficient of thermal expansion,bending strength, and flexural modulus of elasticity of ComparativeExamples 3 to 5 as described below, it is understood that the scale-likegraphite-PPS resin mixture obtained by powder mixing with a ball mill inExample 4 was formed so that the scale-like graphite was dispersed bydelamination while maintaining the average planar particle size.

Examples 5 to 7 and Comparative Examples 3 to 5

High filler-loaded high thermal conductive materials were obtained bythe same method as that used in Example 1, except that the compositionswere prepared at the compositions of Table 2, and raw materials weremixed for 3 minutes with a mixer (swift electric coffee mill), or rawmaterials were inserted into a bag and mixed by manually shaking (handblending) for 5 minutes so as to be sufficiently mixed. The density,thermal conductivity, electrical conductivity, coefficient of thermalexpansion, bending strength, flexural modulus of elasticity, heat offusion per resin, and heat of fusion per filler of each of the specimens(molded articles) thus obtained were measured by the same methods asdescribed above. The results thus obtained are presented in Table 2.

TABLE 2 Comparative Example Example 5 6 7 3 4 5 Com- PPS powder (wt %)50 25 10 50 25 10 position Scale-like graphite 50 75 90 50 75 90 (wt %)Mixing method Mixer/powder Hand blending/ mixing powder mixing Averageparticle 20 to 20 to 20 to 20 to 20 to 20 to size (μm) 80 80 80 200 200200 Molded Density (g/cm²) 1.67 1.91 1.89 1.66 1.75 1.78 article Thermalconductivity 12.5 26.8 40.7 10.8 17.8 2.45 (W/mK) Surface electrical0.15 21.0 67.1 17.2 46.6 103 conductivity ((Ωcm)⁻¹) Cross-section 0.046.09 18.9 6.14 20.3 29.8 electrical conductivity ((Ωcm)⁻¹) Coefficientof thermal 35.5 20.6 8.04 35.7 33.4 30.3 expansion (×10⁻⁶° C.⁻¹) Bendingstrength 49 45 25 33 14 3.7 (MPa) Flexural modulus 2.6 3.1 2.8 2.0 0.820.33 of elasticity (GPa) Heat of fusion per 36 33 16 28 20 15 resin (J/gresin) Heat of fusion per 18.0 24.8 14.4 14.0 15.0 13.5 filler (J/gresin)

From the results of Examples 1 to 7 and Comparative Examples 3 to 5, itwas found that the values of thermal conductivity increased as theconcentration of the thermally conductive filler (scale-like graphite)increased, except for Comparative Example 5. Furthermore, the Examplesgave superior results to the Comparative Examples. Also, with referenceto the results of Examples 1 to 6 and Comparative Example 1, the bendingstrength and the flexural modulus of elasticity had almost the samevalues. The mixing force was such that ball mill>mixer>>hand blending.These results imply that the bending strength and the flexural modulusof elasticity depend strongly on the uniform miscibility at the time ofmixing. Meanwhile, particularly in Example 7, Comparative Example 4 andComparative Example 5 having high filler concentrations, the values ofthe bending strength and the flexural modulus of elasticity markedlydecreased.

Furthermore, with reference to the results of Comparative Examples 3 to5, since shear force almost does not work at the time of mixing in handblending, mixing between the organic polymer particles and the thermallyconductive filler at the level of fine particles occurs insufficiently,so that the organic polymer does not sufficiently penetrate in betweenthe filler particles, and this leads to a decrease in density at thesame filler concentration. For this reason, vacant spaces (voids)between the filler particles could not be sufficiently eliminated, andthis led to significant decreases in the thermal conductivity, bendingstrength and flexural modulus of elasticity.

The thermal conductivity increases almost linearly with theconcentration of the thermally conductive filler; however, theelectrical conductivity increases exponentially, and is stronglyaffected by the properties of the resin, or morphology thereof in thesystem. The specimens of the Comparative Examples show higher valuesthan the Examples. The reasons for this are considered to be as follows:since shear force at the time of mixing is weak, there is almost nodamage in the filler; and when electrical conduction paths are formedeven in some part, a large amount of electric current may easily flowfrom the paths. The electrical conductivities in the ComparativeExamples are higher than the electrical conductivities in the Examples;however, since the thermal conductivity or mechanical properties havebeen significantly deteriorated, the Comparative Examples have nopractical value.

Furthermore, in regard to the coefficient of thermal expansion, thevalue decreases significantly together with the thermally conductivefiller concentration in the Examples, but the extent of the decrease islow in the Comparative Examples. This is speculated to be because in theExamples, a phase A formed from the organic polymer only and a phase Bcontaining a filler as a main component are entangled, the phase B formsa three-dimensional network structure to form a thermally conductiveinfinite cluster; however, in the Comparative Examples, the extent ofthe formation is weak.

Comparative Examples 6 to 11

In regard to a composition containing organic polymer particles and athermally conductive filler, the organic polymer particles and thethermally conductive filler were subjected to melt mixing pelletizationor melt mixing sheet fabrication, and thus a composition that had beenproduced into a pellet or a sheet, is produced (the organic polymerparticles in the composition are not in the form of particles). Thereby,high filler-loaded high thermal conductive materials were produced.

A PPS pellet and a PPS sheet at predetermined concentrations wereproduced by melt kneading at a temperature of 280° C. to 340° C. using atwin-screw extruder (KZW20-30MG manufactured by Technovel Corp).Specifically, pellets having the compositions of Table 3 were producedusing the PPS pellet and scale-like graphite. Subsequently, the pelletswere respectively cooled and solidified for 0.1 hours at a press settingtemperature of 320° C., after a preheating time of 10 minutes under apressurization condition of 3.6 MPa (36.7 kgf/cm²), using a mold havinga size of 120 mm in length×70 mm in width×5 mm in thickness and a hotpressing machine. Thus, high filler-loaded high thermal conductivematerial specimens were produced (Comparative Examples 6 to 8).

Furthermore, sheets were produced to have the compositions of Table 3using a PPS powder and scale-like graphite, and using a T-die for sheetproduction (100 mm in width×16 mm in thickness). Subsequently, thesheets were respectively press molded under pressure and under heatingaccording to Comparative Example 6 using a mold and a hot pressingmachine to produce high filler-loaded high thermal conductive materialspecimens (Comparative Examples 9 to 11).

The density, thermal conductivity, electrical conductivity, coefficientof linear expansion, bending strength, flexural modulus of elasticity,heat of fusion per resin, and heat of fusion per filler of each of thespecimens (molded articles) thus obtained were measured by the samemethods as described above. The results thus obtained are presented inTable 3.

TABLE 3 Comparative Example 6 7 8 9 10 11 Twin- PPS pellet (wt %) 70 5030 screw PPS powder (wt %) 70 50 30 extrusion Scale-like graphite 30 5070 30 50 70 (wt %) Mixing method Twin-screw extrusion/melt mixing Shapeafter extrusion Pellet Sheet Molded Density (g/cm²)    1.42    1.70   1.75    1.40    1.70    1.75 article Thermal conductivity    1.05   5.43    6.00    1.04    4.55    6.23 (W/mK) Surface electrical  <10⁻⁷ <10⁻⁷    0.007  <10⁻⁷  <10⁻⁷    0.007 conductivity ((Ωcm)⁻¹)Coefficient of linear   35.4   33.8   30.5   45.2   40.4   35.2 thermalexpansion (×10⁻⁶° C.⁻¹) Bending 45 42 40 43 40 39 strength (MPa)Flexural modulus   5.3   7.0 11   5.5   7.2 12 of elasticity (GPa) Heatof fusion per 25 23 20 35 33 30 resin (J/g resin) Heat of fusion per  7.8   7.5   9.1   9.0   10.0   12.6 filler (J/g resin)

From the results of Comparative Examples 6 to 11, in the melt mixingusing a twin-screw extruder, the thermal conductivity and the electricalconductivity values were markedly lower, and controllability of thecoefficient of thermal expansion by the filler concentration was alsoinferior, compared with Examples 1 to 7. Thus, it is understood that athermally conductive infinite cluster is not formed. It is speculatedthat the values of the bending strength and the flexural modulus ofelasticity are high because in the sea-island structure of the organicpolymer and the filler, the organic polymer phase forms the sea.

Examples 8 to 13

High filler-loaded high thermal conductive materials were obtained atthe compositions of Table 4 by the same method as that used in Example1, by newly providing a polyethylene terephthalate (PET) powder and apolycarbonate (PC) powder (Examples 8 to 13).

The density, thermal conductivity, electrical conductivity, coefficientof linear expansion, bending strength, flexural modulus of elasticity,heat of fusion per resin, and heat of fusion per filler of the specimens(molded articles) thus obtained were measured by the same methods asdescribed above. The results thus obtained are presented in Table 4.

Meanwhile, in regard to PC which is a non-crystalline aromatic resin,the heat of fusion of the raw material powder exhibited a high valuesuch as 26 J/g resin, but the molded article did not exhibit anendotherm peak that represents the melting point. Thus, the moldedarticle was annealed for 2 hours at 180° C. to 240° C., and an endothermpeak corresponding to the melting point appeared. Therefore, this wasdetermined as the heat of fusion. Table 4 presents this value.

TABLE 4 Example 8 9 10 11 12 13 Com- PET powder 50 25 10 position (wt %)PC powder 50 25 10 (wt %) Scale-like 50 75 90 50 75 90 graphite (wt %)Mixing Ball mill/powder mixing method Average 20 to 20 to 20 to 20 to 20to 20 to particle size 200 200 100 80 80 80 (μm) Molded Density 1.631.88 2.01 1.49 1.79 2.03 article (g/cm²) Thermal 11.7 34.8 48.3 7.7118.7 42.9 conductivity (W/mK) Surface 7.72 32.2 110.5 2.00 7.44 77.9electrical conductivity ((Ωcm)⁻¹) Cross- 2.50 9.64 35.6 0.83 2.06 19.3section electrical conductivity ((Ωcm)⁻¹) Coefficient 31.4 16.8 5.0640.3 24.2 9.56 of thermal expansion (×10⁻⁶° C.⁻¹) Bending 26 31 33 50 4817 strength (MPa) Flexural 1.7 2.0 1.9 3.2 3.4 1.7 modulus of elasticity(GPa) Heat of 24 14 13 0.7 3.2 1.4 fusion per resin (J/g resin) Heat of12.0 10.5 11.7 0.4 2.4 1.3 fusion per filler (J/g resin)

With reference to the results of Examples 8 to 13, similar results toExamples 1 to 4 were obtained, and thus it is understood that theExamples are superior to the Comparative Examples.

Examples 14 to 19

A low molecular weight polyethylene (PE) powder and benzoxazine werenewly provided, and high filler-loaded high thermal conductive materialswere obtained at the compositions of Table 5 by the same method as thatused in Example 1 (Examples 14 to 19).

The density, thermal conductivity, electrical conductivity, coefficientof linear expansion, bending strength, flexural modulus of elasticity,heat of fusion per resin, and heat of fusion per filler of each of thespecimens (molded articles) thus obtained were measured by the samemethods as described above. The results thus obtained are presented inTable 5.

Meanwhile, benzoxazine, which is a thermosetting resin, is a precursor(oligomer) of polybenzoxazine. The heat of fusion of the raw materialwas 25 J/g, but an endotherm peak corresponding to the heat of fusion ofa molded article using this raw material was not observed. It iscontemplated that except for the peripheries of the thermally conductivefiller particles, the cured product was brought to an amorphous statewith the progress of the curing reaction.

TABLE 5 Example 14 15 16 17 18 19 Com- PE powder 50 25 10 position (wt%) Benzoxazine 6 10 5 (wt %) PPS powder 40 (wt %) Scale-like 50 75 90 5490 95 graphite (wt %) Mixing Ball mill/powder mixing method Average 20to 20 to 20 to 20 to 20 to 20 to particle 70 70 70 60 60 60 size (μm)Molded Density 1.24 1.60 2.23 1.64 1.81 1.65 article (g/cm²) Thermal3.12 25.5 39.0 18.9 44.0 42.0 conduc- tivity (W/mK) Surface 0.18 9.5616.6 19.8 66.0 286 electrical conduc- tivity ((Ωcm)⁻¹) Cross- 0.05 2.815.51 5.56 25.0 40.0 section electrical conduc- tivity ((Ωcm)⁻¹)Coefficient 47.6 24.5 10.2 30.4 2.55 2.02 of thermal expansion (×10⁻⁶°C.⁻¹) Bending 13 18 25 43 49 53 strength (MPa) Flexural 0.61 0.97 2.53.2 4.0 5.5 modulus of elasticity (GPa) Heat of 40 31 12 15 0 0 fusionper resin (J/g resin) Heat of 20.0 23.3 10.9 8.1 — — fusion per filler(J/g resin)

With reference to the results of Examples 14 to 19, the same results asin Examples 1 to 4 were obtained, and thus it is understood that theExamples are superior to the Comparative Examples.

Examples 20 to 23 and Comparative Examples 12 and 13

A boron nitride (BN) powder and an aluminum nitride (AIN) powder werenewly provided, and high filler-loaded high thermal conductive materialswere obtained at the compositions of Table 6 by the same method as thatused in Example 1 (Examples 20 to 23 and Comparative Examples 12 and13).

The density, thermal conductivity, electrical conductivity, heat offusion per resin, and heat of fusion per filler of each of the specimens(molded articles) thus obtained were measured by the same methods asdescribed above. The results thus obtained are presented in Table 6. Theelectrical conductivity was measured by a double ring electrode methodusing a high resistivity meter (high resistivity meter manufactured byMitsubishi Chemical Analytech Co., Ltd., HIRESTOR UX type MCP-T800).

TABLE 6 Examples and Comparative Comparative Example Example Examples 2021 22 23 12 13 Com- PPS powder (wt %) 50 25 10 20 50 10 position BNpowder (wt %) 50 75 90 70 AIN powder (wt %) 50 90 Scale-like graphite 10(wt %) Mixing method Ball mill powder mixing Average particle 5 to 5 to5 to 5 to 0.2 to 0.2 to size (μm) 12 12 12 40 2.0 2.0 Molded Density(g/cm²)    1.74    1.95    1.96    1.97    1.75    2.06 article Thermal   8.50   17.1   24.0   18.6    0.98    1.68 conductivity (W/mK)Electrical  <10⁻¹⁴  <10⁻¹⁴ 4 × 7 ×  <10⁻¹⁴ 4 × conductivity <10⁻¹⁴<10⁻¹⁴ <10⁻¹⁴ ((Ωcm)⁻¹) Coefficient of   39.5   18.4    7.63   15.0  38.4 Sampling thermal expansion not (×10⁻⁶° C.⁻¹) possible Bendingstrength 44 46 30 40 65   5.9 (MPa) Flexural modulus   8.4   10.2   7.6  6.3   7.6   1.9 of elasticity (GPa) Heat of fusion per 25 22   5.5 2418   4.9 resin (J/g resin) Heat of fusion per   12.5   16.7   5.0   19.2  11.0   4.4 filler (J/g resin)

When compared with Comparative Examples 12 and 13 in which aluminumnitride that does not have a graphite-like structure and has a highthermal conductivity in a single sintered product, the highfiller-loaded high thermal conductive materials of Examples that usedhexagonal boron nitride having a graphite-like structure as a thermallyconductive filler, produced excellent results similarly to Examples 1 to4. In addition, in Comparative Example 13, the mechanical strength ofthe molded article specimen was weak, a sample for measuring thecoefficient of thermal expansion could not be produced, and thecoefficient of thermal expansion could not be measured.

Comparative Examples 14 to 19

Short carbon fiber was newly provided, and high filler-loaded highthermal conductive materials were obtained at the compositions of Table7 by the same method as that used in Example 1 (Comparative Examples 14to 19).

The density, thermal conductivity, electrical conductivity, bendingstrength, flexural modulus of elasticity, heat of fusion per resin, andheat of fusion per filler of each of the molded article specimens thusobtained were measured by the same methods as described above. Theresults thus obtained are presented in Table 7. Meanwhile, Table 7indicates the fiber size instead of the particle size of thecomposition.

TABLE 7 Comparative Example 14 15 16 17 18 19 Com- PPS powder (wt %)50   25   10   50   25   10   position Short carbon 50   75   90   50  75   90   fiber (wt %) Mixing method Ball mill dry mixing Hand blendingdry mixing Fiber size: Inner 9 to 11, 9 to 10, 1 to 10, About 11, About11, About 11, diameter (μm) 500 to 100 to 10 to 1000 to 1000 to 1000 toLength (μm) 2000 500 50 5000 5000 5000 Molded Density (g/cm²)  1.63 1.85  1.59  1.67  1.92  1.87 article Thermal  3.14 16.6 11.5  4.26 17.026.8 conductivity (W/mK) Surface electrical  8.78 66.5 82.9  2.93 75.2409   conductivity ((Ωcm)⁻¹) Cross-section  2.31 19.2 21.5  1.04 27.398.8 electrical conductivity ((Ωcm)⁻¹) Bending strength 63   73    9.754   62   33   (MPa) Flexural modulus  4.0  4.4  0.46  4.3  3.9  0.96 ofelasticity (GPa) Heat of fusion per 28   14    2.8 22   18   11   resin(J/g resin) Heat of fusion per 14.0 10.5  2.5 11.0 13.5  9.9 filler (J/gresin)

From the results of Table 7, the carbon fiber having a similar graphitestructure to graphite was such that when a ball mill was used uponmixing with PPS, the fiber was markedly damaged, the size was alsodecreased extremely, and the thermal conductivity and mechanicalstrength were markedly decreased particularly at the time of beinghighly loaded. On the other hand, in hand blending mixing, the shape wasmaintained; however, when compared with Examples 1 to 4, the thermalconductivities were markedly decreased. As such, alone use of shortcarbon fiber produced results that were overall inferior to the resultsof the Examples of the present invention. In addition, except forComparative Example 19 in which the content of the short carbon fiberwas 90% by weight, the short carbon fiber had an effect of increasingthe mechanical strength, and it is possible to use the short carbonfiber as a reinforcing material to the extent that the use does notcause contradiction to the purpose of the present invention. Meanwhile,a SEM photograph of a short carbon fiber-PPS resin mixture obtained whenpowder mixing was carried out with a ball mill of Example 16, and a SEMphotograph of the short carbon fiber used as a raw material are shown inFIG. 11 and FIG. 12. From the results of FIG. 11 and FIG. 12, it wasfound that when the short carbon fiber was pulverized and mixed togetherwith a PPS resin in a ball mill, the short carbon fiber was micronizedby losing its rod-shaped structure. That is, it is understood that shortcarbon fiber cannot maintain the average planar particle size of theshort carbon fiber due to delamination. Also, it is contemplated thatthe short carbon fiber having a rod-shaped structure does not overlapsatisfactorily with the plane crystal faces of the PPS resin, unlikegraphite having a structure of a flat shape, a scale shape or the like.It is speculated that this is causative of a marked decrease in thethermal conductivity.

Reference Examples 1 to 7

From the results of Examples 1 to 23 and Comparative Examples 1 to 19,the relationship between the filler concentration and thermalconductivity, the relationship between the filler concentration andelectrical conductivity, the relationship between the fillerconcentration and the heat of fusion per resin, the relationship betweenthermal conductivity and the heat of fusion per filler, and therelationship between the filler concentration and the coefficient ofthermal expansion were plotted based on the data for mixing with (1) PPSpowder-GF/ball mill, (2) PPS powder-GF/mixer, (3) PPS powder-GF/handblending, (4) PPS powder-GF/twin-screw extrusion, (5) PPSpellet-GF/twin-screw extrusion, (6) PET powder-GF/ball mill, (7) PCpowder-GF/ball mill, (8) PE powder-GF/ball mill, (9) benzoxazine-GF/ballmill, (10) benzoxazine-PPS powder-GF/ball mill, (11) PPS powder-BN/ballmill, (12) PP powder-aluminum nitride/ball mill, (13) PPS powder-carbonfiber/ball mill, and (14) PPS powder-carbon fiber/hand blending. Therespective data are shown in FIGS. 1 to 8 as Reference Examples 1 to 8.Meanwhile, the figures include experimental data that are not describedin the Examples and Comparative Examples for better understanding.

In FIGS. 1 to 3, the thermal conductivity increases linearly with thefiller concentration except for the Comparative Examples, and the orderwas as follows:(1)>(10)÷(6)>(2)÷(7)÷(8)÷(9)>(11)÷(14)>(13)÷(3)>(4)÷(5)>(13).Furthermore, it is understood that except for the short carbon fiber(13) and (14), the values of thermal conductivity of the Examples arehigher, and the thermal conductivities are superior to the thermalconductivities of the Comparative Examples.

With reference to FIG. 4, the surface electrical conductivity increasesexponentially in the relationship with the filler concentration, and theorder is almost as follows:(14)>(13)÷(6)÷(3)>(1)>(2)>(7)>(8)>(4)÷(5)>>(11)÷(12). Some parts may bedifferent; however, the surface electrical conductivity is approximatelycorrelated to the thermal conductivity, and the curve rises from afiller concentration of about 40% by weight, and this point is indicatedas the percolation threshold. Also, descriptions on the differencebetween electrical conductivity and thermal conductivity are given inthe discussion on the experimental results of Examples 1 to 7 andComparative Examples 3 to 5.

With reference to FIG. 5, the heat of fusion per resin decreases withthe filler concentration in the following order:(1)÷(2)÷(3)>>(13)>(14)÷(4)>(5). Thus, the order is ball mill÷mixer>handblending>twin-screw extrusion. Also, in the cases of carbon fiber (13)and (14), the heat of fusion significantly decreases at high fillerconcentrations. When pulverization and mixing is carried out with a ballmill, the brittle short carbon fiber undergoes a significant decrease inthe particle size, and therefore, the degree of crystallization of PPSdecreased. Compared with this, there was no decrease in the particlesize in the case of the mixer, but strength decreases due toheterogenization. It is speculated that the heat of fusion per resinincreases more than that of the raw material at a filler concentrationof 20% to 50% by weight, because the degree of crystallization increasesdue to molding under pressure.

In FIG. 6 and Table 5, the heat of fusion per resin decreases almost inthe order of (8)>(6)÷(11)÷(12)>>(7), and the heat of fusion per resindecreases in the order of aromatic crystalline resins (1), (2) and(6)>>aromatic non-crystalline resin (7)>>benzoxazine (9) and (10). Also,the heat of fusion per resin for boron nitride was slightly larger thanthe case of aluminum nitride. It was found that except for specialcases, the heat of fusion per resin is closely related to the thermalconductivity. That is, it is speculated that the heat of fusion perresin of polyethylene which is a crystalline non-aromatic resin is highbecause the resin is a low melting point polyethylene, and a lowmolecular weight polymer having a wide molecular weight distribution(the width of the endotherm peak is also broad). On the other hand, inregard to polycarbonate, the raw material has a high heat of fusion(when condensation polymerization is carried out, an optimal moleculararrangement that can be easily crystallized is possible); however, it isspeculated that in a molded article, an endotherm peak barely appearsdue to aging, and crystallization occurs in the vicinity of the fillerparticles. Furthermore, also for benzoxazine, an endotherm peak based onthe melting point appears in the raw material; however, the endothermpeak is lost in a molded article due to thermal curing. It is speculatedto be because bulky parts that are separated from the filler surfacesbecome amorphous due to thermal curing. In conclusion, since it isspeculated that as crystallization occurs in the vicinity, particularlyalong the surface direction, of the thermally conductive filler having agraphite structure, the filler end faces can be fixed to form thermalconduction paths formed at a high level. Therefore, the magnitude ofthermal conductivity is closely related to crystallization of the resin.

FIG. 7 shows the relationship between the thermal conductivities ofaromatic crystalline resins excluding polycarbonate and polyethylene,and the heat of fusion per filler, separately for Examples andComparative Examples. It is understood that thermal conductivityincreases with an increase in the heat of fusion per filler.Furthermore, it is implied that except for some parts, Examples aresuperior to Comparative Examples, and the thermal conductivity isclosely related to the heat of fusion of the resin. It is speculatedthat a neat linear relationship is not established because the gasbubbles at the filler-resin interface (density), the force of crystals(rigidity) and the like vary subtly depending on the fillerconcentration, molding conditions and method, the kind of resin, and thelike, and this variation largely affects the thermal conductivity.

FIG. 8 illustrates the relationship between the filler concentration andthe coefficient of thermal expansion. The coefficients of thermalexpansion of (1), (2), (6), (7) and (8) decrease with the fillerconcentration from the values in the case of resin alone and approachthe values in the cases of filler alone (about 2×10⁻⁶° C.⁻¹ forgraphite). From this, the filler-loaded resin molded articles of theExamples can be controlled so as to decrease the difference in thecoefficient of thermal expansion with semiconductor elements or ceramicsubstrates (3×10⁻⁶ to 8×10⁻⁶° C.⁻¹), or the difference in thecoefficient of thermal expansion with metals such as copper (17×10⁻⁶°C.⁻¹) and aluminum (24×10⁻⁶° C.⁻¹). On the contrary, it is understoodthat in (3), (4) and (5), the degree of change is small, and it isdifficult to control.

Examples 24 to 27

A composition of BN:PPS (90%:10% by weight) and compositions of GF:PPS(90%:10% by weight, 60%:40% by weight, and 40%:60% by weight) were newlyprovided by the same method as that used in Example 1.

These compositions were separately loaded in a mold having a size of 40mm in length×40 mm in width at the percentage by volume (volume %)indicated in Table 8 so as to form a multilayer structure having athickness of 10 mm, and integrated molding of different materials orintegrated molding of different/gradient materials was carried out usingthe same method as that used in Example 1. Thus, molded articlespecimens having an insulating material and a conductive materiallaminated therein were produced (Examples 24 to 26). Meanwhile,regarding the gradient materials, various GF-PPS layers (thecoefficients of thermal expansion are 2.06×10⁻⁶, 22.4×10⁻⁶, and40.5×10⁻⁶° C.⁻¹, respectively) were filled in the mold in the order thatthe coefficient of thermal expansion is closer to that of a BN-PPS layer(7.63×10⁻⁶° C.⁻¹).

Furthermore, a specimen (molded article) in which an electricallyconductive material was bonded to an insulating material with anadhesive was produced by separately molding a BN-PPS layer and a GF-PPSlayer with the composition of Table 8, and bonding the both with anadhesive agent (ARON ALPHA (registered trademark)) (Example 27).

The density of the specimen (molded article) thus obtained, the thermalconductivity from the BN and GF layer side, the surface electricalconductivity from the GF layer side, the electrical conductivity fromthe BN side, and the bending strength and flexural modulus of elasticityfrom the BN side were measured by the same methods as those used inExample 1. The results thus obtained are presented in Table 8.

TABLE 8 Example 24 25 26 27 Composition BN(90)-PPS(10) layer 20 10 10 20(vol %) GF(90)-PPS(10) layer 30 10 (vol %) GF(60)-PPS(40) layer 80 30 4080 (vol %) GF(40)-PPS(60) layer 30 40 (vol %) Molded Bonded state ofIntegrated Adhesive article different materials molding Density (g/cm²)1.62 1.79 1.77 1.69 Thermal conductivity 23.2 22.4 20.8 4.44 from BNside (W/mK) Thermal conductivity 25.3 20.3 18.2 16.23 from GF side(W/mK) Electrical 6 × 6 × 6 × <10⁻¹⁴ conductivity from BN 10⁻¹⁴ 10⁻¹⁴10⁻¹⁴ side ((Ωcm)⁻¹) Surface electrical 33.6 7.93 6.21 12.9 conductivityfrom GF side ((Ωcm)⁻¹) Bending strength 25 37 40 25 from BN side (MPa)Flexural modulus of 1.5 2.2 2.5 0.8 elasticity from BN side (GPa)

According to the comparison between Example 24 and Example 27,integrated molding and bonding with an adhesive have a significantdifference in the thermal conductivity, and it is understood that aproduct obtained by integrated molding is superior. Measurement of thethermal conductivity by a hot disc method is to determine the thermalconductivity in the vicinity of the surface of a specimen having acertain depth, and therefore, the BN side and the GF side have differentthermal conductivities. Since the thermal conductivity of theBN(90)-PPS(10) layer alone is 24.0 W/mK, this is almost consistent withthe thermal conductivity from the BN side of the integrated moldedproduct. Thus, no decrease was observed in the thermal conductivity atthe interface between the GF-PPS layer and the BN-PPS layer. When themolded articles were bonded with an adhesive, it is speculated that thethermal conduction properties on the adhered surface is markedlydecreased, so that a significant decrease in the thermal conductivity.The thermal conductivity from the GF side of Example 24 almost reflectsthe thermal conductivity of the GF(60)-PPS(40) layer alone; however, thelow value of the thermal conductivity of Example 27 is believed to havebeen affected by the adhered interface. In regard to the electricalconductivity, the BN side is an insulator in the order of 10⁻¹⁴, withthe electrical conductivity being measured with a high resistivitymeter, and the GF side exhibits surface electrical conductivity measuredwith a low resistivity meter and is an electrical conductor. Theelectrical conductivity on the BN side implies that the BN side is aninsulator under the effect of the BN-PPS layer, and thus this moldedarticle can be used as a semiconductor substrate. Also in Examples 25and 26 in which the GF-PPS layer was formed from a three-phase gradientmaterial, excellent results were obtained similarly to Example 24. Thus,it is understood that bonding can be achieved by reducing the differencein the coefficient of thermal expansion between the BN-PPS layer and theGF-PPS layer, and reducing the difference in the coefficient of thermalexpansion between the GF side and metals such as aluminum and copper.

Examples 28 and 29

Accordingly to Example 1, a GF-PPS resin composition (electricallyconductive) having a GF concentration of 60% by weight was produced, andthe composition was loaded into a mold having a size of 40 mm inlength×40 mm in width. Thus, a molded article having a thickness of 9.5mm was produced. Separately, a PPS resin composition having a BNconcentration of 90% by weight produced according to Example 22 wasuniformly dispersed in methyl ethyl ketone (MEK) using ultrasonic waves,and thus a 25 wt % MEK coating liquid was produced. The coating liquidwas applied and dried on the surface of the GF-PPS molded article, andthen the molded article was subjected to press molding by heating underpressure in the same manner as in Example 1. Thus, aninsulating/electrically conductive integrated molded article having aBN-PPS layer with a thickness of 0.5 mm was produced. The density,thermal conductivity, electrical conductivity, bending strength, andflexural modulus of elasticity were measured according to Example 24,and these values are presented in Table 9 as Example 28.

On the other hand, tetralin was introduced into a sealed pressure vesselto obtain a PPS content of 20% by weight, and the mixture of PPS andtetralin was heated to 230° C. under sealing to dissolve PPS. Thus, aPPS-tetralin solution was produced. An appropriate amount of t-butanol(TBA) was added to a BN-oxazine composition at a weight ratio of 80:20,which was separately produced according to Example 1, and thus adispersion liquid was produced. The PPS-tetralin solution was added tothis dispersion liquid such that the ratio of PPS:oxazine reached 10:90as a weight ratio, and the mixture was further diluted with TBA. Thus, aTBA-dispersed coating liquid having a BN-(PPS-oxazine) (weight ratio80:(2:18)) content of 25% by weight was produced. This coating liquidwas uniformly dispersed by ultrasonication, and was applied and dried onthe surface of the GF-PPS molded article. Subsequently, the coatingliquid was heated to cure for 3 hours in a vacuum under the pressure of0.5 MPa in a vacuum dryer at 250° C., and thus a molded article coatedwith a BN-oxazine layer having a thickness of 0.5 mm was produced.Various physical properties were measured in the same manner as inExample 28, and these values are presented in Table 9 as Example 29.

TABLE 9 Example 28 29 Composition BN(90)-PPS(10) layer (vol %) 5 —BN(80)-(PPS-oxazine)(20) — 5 layer (vol %) GF(60)-PPS(40) layer (vol %)95 95 Molded Bonded state of heterogeneous Integrated Coating articlematerials molding film Density (g/cm²) 1.65 1.60 Thermal conductivity onBN 25.5 24.2 side (W/mK) Thermal conductivity on GF 26.1 20.5 side(W/mK) Electrical conductivity on BN 7 × 10⁻¹⁴ 8 × 10⁻¹⁴ side ((Ωcm)⁻¹)Surface electrical 35.8 36.5 conductivity on GF side ((Ωcm)⁻¹) Bendingstrength from BN side 33 30 (MPa) Flexural modulus of 2.5 2.0 elasticityfrom BN side (GPa)

Examples 30 to 33

A 60 wt % GF-PPS resin composition (electrically conductive) wasproduced according to Example 28, and a resin molded article blockhaving a size of 149.4 mm in length×149.4 mm in width×34.5 mm inthickness was produced using a square-shaped mold which measured 150 mmin length and width.

This molded article block was subjected to machining, and thereby a GFheat dissipation component of a comb type fin structure having a basalpart measuring 149.4 mm in length and width and a thickness of 12.0 mm,and 15 sheets of rectangular fins each measuring 2.5 mm in thickness,22.5 mm in depth, and 149.4 mm in length arranged thereon at an equalinterval, was produced. The weight of the heat dissipation component was628 g, the surface area was 1544 cm², the specific heat capacity was1.158 J/gK, and the density was 1.892 g/cm². This GF heat dissipationcomponent was bonded with a 7.68-W heater (manufactured by Japan MarinaCo., Ltd., KAPTON HEATER HK9BF) embedded in a polyimide film, without anadhesive, or by sealing with tape, using a silicone grease (thermalconductivity 3.8 W/mK, manufactured by Shenzhen Halnziye ElectronicsCo., Ltd.), or by applying and solid-drying a TBA dispersion coatingliquid formed from the BN-(PPS-oxazine) composition at a weight ratio of80:2:18 used in Example 29, and subsequently performing a thermal curingreaction for 2 hours at 100° C. and then for 3 hours at 230° C. in avacuum. Thus, heat dissipation components were produced, and a heatdissipation test was carried out in a thermostatic chamber at 30° C.Thermocouples were attached to three sites, including the heater part,the fin-rooted basal part, and the fin tips, and the heat dissipationbehavior was measured. Thermal resistance was determined from thetemperature at which an equilibrium state was reached, and the resultsare presented in Table 10 as Examples 30, 31 and 32. At the time pointwhen equilibrium was reached, the temperature inside the thermostaticchamber had been elevated to 37.0° C., and thus the time point wasconsidered as an equilibrium point.

Furthermore, 88.7 g of a BN:PPS (80:20 wt %) composition and 1189.1 g ofa GF:PPS (60:40 wt %) composition were prepared, and a resin integratedmolded article block having a size of 149.4 mm in length×149.4 mm inwidth×34.5 mm in thickness, in which the BN:PPS layer was 2 mm inthickness and the GF:PPS layer was 30 mm in thickness, was producedaccording to Example 24, using a square-type mold measuring 150 mm inlength and width. This molded article block was subjected to machining,and thereby a GF heat dissipation component having a comb-type finstructure having a basal part measuring 149.4 mm in length and width anda thickness of 12.0 mm, and 15 sheets of rectangular fins each measuring2.5 mm in thickness, 22.5 mm in depth, and 149.4 mm in length arrangedthereon at an equal interval, was produced. The weight of the heatdissipation component was 664 g, and the surface area was 1544 cm². Aheat dissipation experiment was carried out in the same manner as inExample 30 to determine the equilibrium temperature and the thermalresistance. The results are presented in Table 10 as Example 33.

TABLE 10 Example and Comparative Example Example 30 Example 31 Example32 Example 33 Kind of comb-type GF heat GF heat GF heat GF heat finstructured dissipation dissipation dissipation dissipation heatdissipation component component component component component Bonding ofheater None Silicone grease BN-(PPS-oxazine) (BN-PPS)-(GF-PPS) andfin-type heat adhesive integrated dissipation unit molding Equilibrium97.6 66.9 66.5 67.2 temperature (T₁) of heater part Equilibrium 47.849.8 50.4 51.1 temperature (T₂) of fin-rooted basal part Equilibrium44.7 46.9 47.7 47.6 temperature (T₃) of fin tip part Atmospheric 37.037.0 37.0 37.0 temperature of constant temperature tank (T₄) Thermal6.48 2.23 1.94 2.10 resistance from T₁ and T₂ (R₁) Thermal 0.40 0.380.35 0.46 resistance from T₂ and T₃ (R₂) Thermal 1.00 1.29 1.39 1.38resistance from T₃ and T₄ (R₃) Thermal 7.88 3.89 3.68 3.94 resistancefrom T₁ and T₄ (R_(T))

It was found from Table 10 that as compared with Example 30 of the casewithout an adhesive, when silicone grease (Example 31), an adhesive(Example 32), and integrated molding (Example 33) were carried out, theequilibrium temperature of the heater part decreased significantly.Also, it was found that in regard to the value of thermal resistance,contribution of the thermal resistance on the heat dissipation to theinterface between the heater and the heat dissipation component (R₂) andto the interface between the heat dissipation component and theatmosphere (R₃) was larger than the contribution of the thermalresistance of the material itself (R₁).

1. A high filler-loaded high thermal conductive material, formed bysubjecting a composition which comprises organic polymer particlescomprising a thermoplastic polymer and a thermally conductive fillerhaving a graphite-like structure, and comprises 5 to 60% by weight ofthe organic polymer particles and 40 to 95% by weight of the thermallyconductive filler having a graphite-like structure relative to 100% byweight of the total amount of these components, is obtained by using apulverizing machine so that the thermally conductive filler is dispersedby delamination while maintaining the average planar particle size ofthe thermally conductive filler, and is capable of forming a thermallyconductive infinite cluster; press molding at a temperature higher thanequal to the deflection temperature under load, melting point or glasstransition temperature of the organic polymer and a pressure of 1 to1000 kgf/cm²; and cooling and solidification.
 2. The high filler-loadedhigh thermal conductive material according to claim 1, wherein thepulverizing machine is a ball mill.
 3. The high filler-loaded highthermal conductive material according to claim 1, wherein thethermoplastic polymer contains at least one selected from the groupconsisting of a thermoplastic resin and a thermoplastic elastomer, allof which have crystallinity and/or aromaticity.
 4. The highfiller-loaded high thermal conductive material according to claim 1,wherein the thermoplastic polymer contains at least one selected fromthe group consisting of polyphenylene sulfide, polyethyleneterephthalate, polybutylene terephthalate, and polycarbonate.
 5. Thehigh filler-loaded high thermal conductive material according to claim1, wherein the organic polymer particles further contain an uncuredthermosetting resin.
 6. The high filler-loaded high thermal conductivematerial according to claim 5, wherein the uncured thermosetting resincontains at least one selected from benzoxazine.
 7. The highfiller-loaded high thermal conductive material according to claim 1,wherein the thermally conductive filler contains graphite.
 8. The highfiller-loaded high thermal conductive material according to claim 7,wherein the graphite contains natural graphite and/or artificialgraphite.
 9. The high filler-loaded high thermal conductive materialaccording to claim 7, wherein the graphite contains scale-like graphite.10. The high filler-loaded high thermal conductive material according toclaim 7, wherein the high filler-loaded high thermal conductive materialhas a thermal conductivity of 10 to 150 W/mK, a coefficient of thermalexpansion of 3×10⁻⁶ to 30×10⁻⁶° C.⁻¹, and a surface electricalconductivity of 5 to 200 (Ωcm)⁻¹.
 11. The high filler-loaded highthermal conductive material according to claim 1, wherein the thermallyconductive filler contains thermally conductive ceramics.
 12. The highfiller-loaded high thermal conductive material according to claim 1,wherein the thermally conductive ceramics contains hexagonal boronnitride.
 13. The high filler-loaded high thermal conductive materialaccording to claim 11, wherein the high filler-loaded high thermalconductive material has a thermal conductivity of 5 to 50 W/mK, acoefficient of thermal expansion of 3×10⁻⁶ to 30×10⁻⁶° C.⁻¹, and anelectrical conductivity of 10⁻¹⁰ (Ωcm)⁻¹ or less.
 14. A highfiller-loaded composition, which comprises organic polymer particlescomprising a thermoplastic polymer and an uncured thermosetting resin,and a thermally conductive filler having a graphite-like structure,comprises 5 to 60% by weight of the organic polymer particles, 40 to 95%by weight of the thermally conductive filler having a graphite-likestructure, and 0 to 6% by weight of the uncured thermosetting resinrelative to 100% by weight of the total amount of these components, isobtained by using a pulverizing machine so that the thermally conductivefiller is dispersed by delamination while maintaining the average planarparticle size of the thermally conductive filler, and is capable offorming a thermally conductive infinite cluster.
 15. A coating liquidcomprising the high filler-loaded composition according to claim 14, anda dispersing medium.
 16. A molded article, comprising the highfiller-loaded high thermal conductive material according to claim 1, andbeing used as a high thermal conduction/heat dissipation component. 17.The molded article according to claim 16, wherein the molded article isformed by laminating two layers of the high filler-loaded high thermalconductive material; one layer of the two layers has a thermalconductivity of 15 to 120 W/mK and a coefficient of thermal expansion of3×10⁻⁶ to 30×10⁻⁶° C.⁻¹, and exhibits electrical conductivity with asurface electrical conductivity of 10 to 200 (Ωcm)⁻¹; and the otherlayer of the two layers has a thermal conductivity of 5 to 50 W/mK ormore and a coefficient of thermal expansion of 3×10⁻⁶ to 10×10⁻⁶° C.⁻¹,and exhibits insulating properties with a surface electricalconductivity of 10⁻¹¹ (Ωcm)⁻¹ or less.
 18. The molded article accordingto claim 17, wherein the layers of the high filler-loaded high thermalconductive material is formed of a gradient material.